Just one in six homes sold under Right to Buy have been replaced, with the scheme resulting in a net loss of more than 10,000 affordable homes last year.
Over the past year nearly 13,000 council homes were sold under Right to Buy, a scheme which gives council tenants big discounts to buy their homes.
However, only 2,200 council houses were built over the same period - despite the Government's pledge to directly replace every home sold.
The trend is set to continue this year, according to fresh statistics from the Department for Communities and Local Government.
In the first quarter of 2016/2017, 3,362 council homes were sold off and just 422 replaced.
Liberal Democrat leader Tim Farron said: "The success or failure of Right to Buy rests on whether every single home is replaced.
"We fought tooth and nail for the Government to commit to one-for-one replacement in the Housing and Planning Bill, and yet in practice it has been more like one for every six sold.
"Yet again, affordable homes are being sold off into private hands and will end up as buy-to-lets, while those in need lose out."
There has been a fresh surge in the number of homes being bought through Right to Buy since 2012, after the Government introduced bigger discounts.
The Government insists Right to Buy plays a big part in its efforts to encourage home ownership, and is now extending the scheme to apply to housing association tenants.
Housing and planning minister Gavin Barwell said: "From London to Leeds, Right to Buy plays an important part in building a country that works for everyone, helping thousands of people become homeowners for the first time.
"And we're determined to replace the additional homes sold on a one-for-one basis, nationally - providing new affordable homes for rent for those who need them."
More than 312,000 households have now used Government-backed home ownership schemes including Right to Buy, Help to Buy and Help to Buy: Shared Ownership since 2010.
Roger Harding, Shelter's director of policy and campaigns, said: "Helping social renters to buy their own home is of course a good thing, but without like-for-like replacement every home sold off through Right to Buy is yet another dent on our already dwindling number of genuinely affordable homes.
"And with the current record of replacement just one home built for every eight sold, these numbers are only going to get lower.
"It doesn't have to be this way. The new Government has a chance to give back hope to all those struggling to keep up with sky-high housing costs and languishing on waiting lists, but only if they commit to measures that will build more homes that people on lower incomes can actually afford."
A spokesman for the Department for Communities and Local Government said: "We've set out the largest affordable housing programme of any Government since the 1970s, doubling the budget to £8bn to deliver 400,000 more homes.
"There's a rolling three-year deadline for councils to replace additional homes sold and so far they've delivered within that.
"However, we've been clear that if they don't, then we'll step in and make sure they get built."