Most of the boroughs in London are failing to build enough affordable homes, a new report by the housing charity Shelter has revealed.
Only five boroughs managed to meet Mayor Ken Livingstone's target of ensuring 50% of all new homes were affordable, the report found.
Wandsworth and Bexley were the worst offenders with only 12% and 15% of homes being affordable, it said.
The report looked at the councils' performances since 2004.
The London Plan, which sets the annual housing targets for councils, states at least half of all new houses built in every borough needs to be affordable and 70% of this social housing has to be kept for rent.
Both Wandsworth and Bexley councils have countered the figures in the report.
The charity adds that about 200,000 families were forced to live in overcrowded houses due to a shortage of suitable houses within their budget.
Adam Sampson, chief executive of Shelter, said: "It is vital councils meet the targets set for affordable housing if hard working Londoners are to have any chance of securing a decent home in the capital.
"The government has pledged to make housing a top priority which means local councils will need to work much harder to ensure they meet these targets and help address the capital's growing housing crisis," he said.
The charity said the five boroughs which managed to meet their 50% targets were Hammersmith and Fulham, Haringey, Waltham Forest, Ealing and Barking and Dagenham.
The worst offenders were Wandsworth, Bexley, Kingston-upon-Thames, Greenwich and Havering.
Dispute over figures
A spokesman for Wandsworth Council said it was "11th highest in building affordable homes, not the lowest."
He said: "We have previously disputed the figures which have been previously quoted by the mayor and an analysis of GLA's (Greater London Authority) own database gives a much different picture."
About 700 new affordable homes have been built in the past three years in Wandsworth. Therefore 16% of all new homes were affordable, the council said.
Bexley Council's cabinet member for regeneration and housing, Councillor John Waters, said: "While we comply with statutory requirements, we have never accepted that a 'one-size-fits-all' approach is correct for the whole of London.
"Therefore the amount of affordable housing in Bexley may well be less than 50%."
The council added that 42% of all new buildings in the area were affordable homes.