The Guardian requested information on empty homes from London councils under the Freedom of Information Act. According to the data collected by the Guardian, 8,561 homes have been empty for over two years and 1,100 have been empty for over a decade.

The number of homes that are actually empty could be higher than what was reflected in the data as there is neither an obligation on homeowners to report empty homes nor an obligation on local authorities to keep a register. Additionally, this data does not include data from Bromley or Westminster Council.

These statistics have been released at a time when London councils are under pressure to build new homes to assist with the capital's housing crisis. Councils can make use of empty properties in a variety of ways; including purchasing them with a compulsory purchase order, assisting with repair costs or charging additional council tax to disincentivise empty properties.

Thinktank, Policy Exchange found that there are over 500 hectares of unused industrial land in the city. It argues that empty properties in the capital should be compulsorily purchased to deliver new homes and the London mayor should be given greater powers to purchase empty commercial properties.

Planning expert Victoria Lindsay of Pinsent Masons, the law firm behind Out-Law.com said: "This is a huge number of vacant properties and the true number is likely to be even higher as Bromley Council did not respond to the freedom of information request and Westminster said it could not supply the dates when properties became empty."

"In the past, councils have attributed a small percentage of vacant properties to the phenomenon known as 'buy-to-leave' where rich investors, often from abroad, purchase property and leave it empty taking advantage of rising property prices. However, more often it is because of ordinary financial concerns and lack of financial resources to renovate a property," said Lindsay.

"Since April 2013, councils have been able to impose a punitive 'empty homes premium' of an additional 50% council tax, thereby disincentivising homeowners from admitting that they are leaving properties empty. Whilst councils do need to have a crack down on taking action against/assisting homeowners who are leaving properties vacant, this is not going to alleviate the housing crisis in London, it will merely assist", said Lindsay.