Private landlords received £9.3bn in housing benefit last year - almost double the amount they did a decade ago, according to a new report.
The increased number of private renters receiving the benefit and the higher costs of private rentals have contributed to the rise, the National Housing Federation (NHF) said.
David Orr, chief executive of the NHF, said it was “madness” that the money was being spent on the private sector and not being invested in affordable homes.
But the Government said it was taking steps to manage the bill.
In 2006, £4.6bn was paid out in housing benefit to private landlords, but since 2008 there has been a 42 per cent rise in the number of private renters receiving housing benefit, according to the NHF analysis.
An additional £1,000 is spent every year on each family renting privately and claiming housing benefit - a £5,705 cost compared with £4,638 for those in the social rented sector, the report said.
In London, £3,300 more is spent every year on each family claiming in the private sector, it added.
The organisation said the Government could save £1.5bn a year if all those housed in the private rented sector lived in affordable housing.
“It is madness to spend £9 billion of taxpayers’ money lining the pockets of private landlords, rather than investing in affordable homes,” Mr Orr said.
“Housing associations want to build the homes the nation needs. By loosening restrictions on existing funding, the Government can free up housing associations to build more affordable housing at better value to the taxpayer and directly address the housing crisis.”
A Government spokesman said it had taken action to reduce the private rental sector housing benefit bill.
“The reality is we have taken action to bring the housing benefit bill under control, and since 2012 the amount going to private sector landlords has actually been falling - something which the National Housing Federation fails to recognise,” he said.
“We are also committed to building the homes this country needs and investing £8 billion to build 400,000 more affordable homes.”