The London mayor has accused Conservative and Liberal Democrat councils of refusing to build social housing to prevent Labour supporters moving in to marginal wards.

In his address to the Labour Party conference on Wednesday Ken Livingstone threatened to use his compulsory purchase powers to ensure affordable homes were provided to ease the capital's housing crisis.

Blaming Margaret Thatcher for stopping the construction of council housing, Livingstone vowed to help more low-income families get stable, long-term accommodation.

Livingstone, who faces an election next year, cited the example of the Lib Dem/Tory-run Southwark council, which he said was blocking development of brownfield land near City Hall for political reasons.

"The council refuses to sell the strip of land to allow the development to proceed," he said.

"Four years have passed and an empty site, in the heart of the city in the borough of Southwark - which has tens of thousands on the waiting list - and still nothing being built."

He also rubbished his probable Tory opponent Boris Johnson's claim that the housing shortage was caused by the mayor's affordable housing target.

"It is not the affordable housing target that prevents housing being built, it is Tory and Lib Dem councils blocking the development of housing because they think it will change the political complexion of the ward in which it is being built," Livingstone said.

"I say to Southwark Council now that if you can't agree within the next month to do a deal with the developer so we build housing on that site it will be the first time I have had to ever impose a compulsory purchase order on borough council-owned land."