LONDON – New analysis shows that there are close to 20,000 homes sitting empty in London, with ten times that number unoccupied across the UK.

Property investment marketplace Property Partner analysed figures from the Department of Communities and Local Government on “long-term vacant dwellings” in England and Wales between 2006 and 2016.

London emerges as the vacant home capital of the country, with 19,845 homes sitting idle for over six months in 2016. Across England, there were 200,145 empty homes.

The number of “ghost” homes in London has declined since last year when the Guardian found over 22,000 idle homes in the capital. But Property Partner estimates that the combined value of the property still sitting empty in the capital is £9.4 billion ($12 billion).

The large number of empty houses in the capital also come at a time of rising homelessness in the UK. The number of people sleeping rough has risen by 54% since 2010, according to government figures released in the middle of last year. Homeless charity Shelter estimated in December that there are at least 255,000 homeless people in England. 18 of the top 20 area with the most homelessness are in London.

Houses and flats can be left empty for a variety of reasons. Homelessness charity Empty Homes says on its website: "Some of these [empty homes] may not stay empty (if they are on the market, or are being renovated). But others are stuck empty, perhaps because of inheritance issues or because their owners are holding on to the property hoping for a rise in its value before selling it."

The hotspot for "ghost" houses - those left empty to appreciate in value - is in the affluent borough of Kensington & Chelsea in London, where 1,399 houses sit empty. The number represents an 8.5% rise on 2015 and a 22.7% rise between 2006 and 2016.

Kensington & Chelsea is a hotspot for so-called "buy-to-leave" property deals, where wealthy foreign investors purchase properties as investments and leave them to sit empty as their value increases. Both the Evening Standard and the Guardian have dubbed Kensington & Chelsea a "ghost town" in recent years due to this practice.

A Freedom of Information request in 2013 found that just 19 out of 80 apartments in One Hyde Park in Kensington were occupied. The rest were either empty or second homes. One Hyde Park was at the time the most expensive residential development in the UK, with apartments costing up to £100 million each.

Despite stamp duty changes, the practice of "buy to leave" appears to be continuing. A recent Transparency International report found that less that a quarter of homes built in 14 recent London developments were sold to UK buyers. Every flat sold so far in the redevelopment of the Heygate Estate in south London has gone to foreign investors, according to the report.

Perhaps surprisingly, the area with the second highest concentration of empty houses in London is Croydon. The outer London borough had 1,216 empty homes in 2016. That is down from a high of 2,721 in 2006.

Croydon is not traditionally seen as a good area - it has been called "London's punchline" - but rising house prices in inner London and the construction of a new Westfield's shopping centre in the area have led to a building boom, with a large number of new homes constructed in the area. It is not clear whether the large number of empty homes is down to new housing stock that has yet to be sold, investors snapping up property in the area, or some other factor.

Over the last decade, Property Partner found the number of long-term vacant homes in England dropped 36.4% from 314,719 in 2006. The estimated value of empty property in England stands at £43.5 billion.