A third of the mansions on the most expensive stretch of London's "Billionaires' Row" are empty, including several that have fallen into ruin after standing almost completely vacant for a quarter of a century.
There are an estimated £350 million (HK$4.5 billion) worth of vacant properties on the most prestigious stretch of The Bishops Avenue in north London, which last year was ranked the second most expensive street in Britain.
One property owner, the developer Anil Varma, has complained that the address has become "one of the most expensive wastelands in the world".
The empty buildings include a row of 10 mansions that have stood largely unused since being bought between 1989 and 1993, it is believed on behalf of members of the Saudi royal family.
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.
Most of the properties in the most expensive part of the avenue are registered to companies in tax havens including the British Virgin Islands, Curacao, the Bahamas, Panama, and the Channel Islands, allowing international owners to avoid paying stamp duty on the purchase and to remain anonymous.
The revelations come at the same time as a growing political row over how empty properties can help solve a national housing shortage growing by more than 100,000 homes a year.
London Mayor Boris Johnson has defied Downing Street to call for taxes to be cranked up on owners of vacant properties.
He told City of London investors last month: "London homes aren't… just blocks of bullion in the sky." He called for owners to live in their homes or rent them out.
But the government has resisted attempts by councils, backed by the mayor, to multiply council tax rates on homes left empty for two years.
"This illustrates everything that is wrong with the London housing market," said David Ireland, chief executive of the Homes from Empty Homes campaign group.
"The high values are being used as an extreme investment vehicle at the expense of homes being homes.
"London's shortage of homes is so great that this feels immoral and dysfunctional. There are countless people in inadequate housing and here are homes on The Bishops Avenue that could be used."