Since 2012, when the discount was increased to £108,000 in London and £80,000 in the rest of the country, 69,467 homes have been sold, the Chartered Institute of Housing revealed in a briefing paper on Tuesday.
But construction has only started on 18,958 to replace those homes sold, the CIH calculated.
The housing body is calling for the policy to be suspended and for the government instead to invest in building more social homes for rent.
Terrie Alafat, CIH chief executive, said: “Not only are we failing to build enough new homes for social rent, we are losing them at a time when we need them more than ever.
“Suspending the scheme means the government could invest the savings in more homes for social rent – which is often the only truly affordable option for people on lower incomes – and also in fairer and more cost-effective ways to help tenants access home ownership.”
CIH research from January found that more than 150,000 social homes for rent in total had been lost between 2012 and 2017 due to right to buy and other factors. It estimated this figure will reach 230,000 by 2020 unless “we take action now”, Alafat said.
Council leaders warned earlier this year that just one third of councils were able to replace homes sold under the scheme in five years’ time.
The Local Government Association called for “fundamental reform” of the scheme and for councils to be allowed to borrow in order to build new homes.
At the Conservative Party Conference this week, prime minister Theresa May scrapped the cap on how much councils can borrow against their housing revenue but has not so far addressed the issue of right to buy.
Other organisation have also called for the right to buy scheme to be suspended because of the loss of social rented homes, the CIH said in the 2018 UK Housing Review.
“About two-thirds of the discount that a tenant who buys their home now receives is justified because they are sitting tenants paying sub-market rent. But one-third is an excessive discount which, if clawed back, would lead to more money coming to councils to build new homes,” Alafat added.
Earlier this year, the government launched a pilot allowing housing association tenants to buy their social homes.
In June, a £1.67bn government grant was announced from the £9bn affordable homes programme to deliver 23,000 new affordable homes, including 12,500 for social rent.
At the end of last year, May pledged an extra £2bn from 2022 for housing associations to help build more homes.
