Fewer than half the homes built to replace thousands sold under right to buy are traditional council homes, new research suggests.
Labour said the findings showed the Conservatives' approach to right to buy discounts for council tenants was "failing".
Figures obtained by Inside Housing magazine show just 48% of the replacements for council homes sold are like-for-like, with many being let out at the more expensive "affordable" rents.
Further figures obtained by the magazine show that only one in five homes sold under the scheme have been replaced.
Shadow housing minister John Healey said: "This confirms the extent to which the Conservatives' damaging approach to right to buy is failing.
"Not only has just one in five homes sold under the right to buy been replaced, but of those that have been replaced fewer than half are let at a genuinely affordable social rent."
The Conservatives upped right to buy discounts in 2012 in a bid to revitalise the flagship policy of former prime minister Margaret Thatcher, which gives council tenants discounts to buy their home.
Then-prime minister David Cameron allowed town halls to keep a portion of the sales receipts to replace those sold.
Research by Inside Housing shows only 10,644 replacements have been started so far, to replace 51,352 homes sold since the higher discounts were introduced.
Freedom of information responses sent to Inside Housing by 111 councils - 75% of those which are building replacements - showed only 48% (3,962) of the 8,109 new homes they had started were at social rents.
"Affordable rent" made up 3,971 of the replacement homes, with the remainder consisting of temporary housing and other types of tenancies.
Affordable rents can be set at up to 80% of the market value - as much as £1,000 a month in parts of London.
Sir Steve Bullock, executive member for housing at London Councils and mayor of Lewisham Council, told Inside Housing: "The restrictions that councils have had to deal with on right to buy receipts have made it unnecessarily difficult to achieve direct one-for-one replacement."
Labour has pledged to suspend right to buy until councils can come up with a plan to provide "like-for-like" replacements for the homes sold.
The Government previously advised councils to replace homes sold with the higher affordable rent when it boosted the discounts, which now stand at £78,600 nationally and £104,900 in London.
Despite this, some councils have provided only social rent replacement homes to meet the needs of their residents.
Conservative-led New Forest Council has delivered 153 right to buy replacements, all at social rents, while Labour-led Islington has provided all its 193 replacements at social rent.