About 133,000 households in London will be unable to afford their rent if proposed changes to the welfare system go ahead, a study has claimed.
The government is capping total benefits for workless couple and single parent households at £500 a week.
The London Councils report warns thousands of families in London will no longer be able to afford their rent.
Ministers say it is unfair unemployed households can get more from benefits than the average working family earns.
The crackdown - which would see benefits for single person households limited at £350 - is intended to save £7bn a year.
The new rules are due to take effect from 2013. They would see the maximum income from benefits capped at the level of the UK median income.
But the new study says the government plans have taken no account of higher housing costs in London.
'Simply isn't fair'
It claims Brent and Redbridge are the boroughs where the most families - some 30% - would not be able to afford their current rent, because they have a greater proportion of larger households.
The authors say many inner London boroughs would also become unaffordable to low income families by 2016.
A London Councils spokesman said: "More than a third of single parent families living in London with three children will not be able to afford their rent.
"Couples with three children will fare even worse, with more than 50% expected to be unable to pay their rent."
A Department for Work and Pensions spokeswoman said: "It simply isn't fair that households on out-of-work benefits can receive a greater income from the state than the average working household gets in wages.
"This is why we have proposed a benefit cap of around £500 per week for couple and single parent households - that's the equivalent of a salary of £35,000 a year before tax.
"Many working-age families with adults in work cannot afford to live in central London, for example, and it is not right for the taxpayer to subsidise households on out-of-work benefits who do."