Bishops Ave houses. Number 46a , Royal Masions. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

Bishops Ave houses. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Georgians' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Redcroft' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Redcroft' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Redcroft' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Redcroft' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Ilkley House' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Redcroft' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Ilkley House' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Ilkley House' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Ilkley House' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine

The Bishops Ave houses that were bought by the Saudi Royal family in the 90's and have been now sold. The house has never been lived in and has been left to rot. Pictured is ' Ilkley House' on The Bishops Ave. A third of the mansions on the most expensive stretch of London's 'Billionaires Row' are standing empty, including several huge houses that have fallen into ruin after standing almost completely vacant for a quarter of a century. An investigation has revealed there are an estimated L350m worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked as the second most expensive street in Britain. The empty buildings include a row of 10 mansions worth L73m which have stood largely unused since they were bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family. Exclusive access to now derelict properties has revealed that their condition is so poor in some cases that water streams down ballroom walls, ferns grow out of floors strewn with rubble from collapsed ceilings, and pigeon and owl skeletons lie scattered across rotting carpets. ? Graeme Robertson / eyevine