The construction of new homes will need to increase "five-fold" to meet the government's one-for-one pledge through the right to buy scheme.
The National Audit Office (NAO) has warned MPs in written evidence supplied to the Public Accounts Committee (PAC) that the current proposals in the Housing and Planning Bill to give 1.3m housing association tenants the right to buy their properties at discounted prices will require the "pace of [replacement]" to significantly accelerate in the coming years.
The housing bill, currently being scrutinised in the House of Lords, stipulates that the right to buy scheme will be financed through the sale of "high-value" council homes when they fall vacant.
However, the bill also pledges for a new replacement home to be available for every property sold by housing associations, as well as additional homes for those sold off by local authorities within three years. In parts of London where there are acute housing shortages, this would rise to at least two additional homes for each one sold.
"Under the Department [for Communities and Local Government]'s objective, housing providers have up to three years from sale of a council property to make a start on using the receipts to provide replacement homes. The Department has taken the housing starts and acquisitions funded by this policy for the three years 2012-13 to 2014-15 together," the NAO report states.
"This yields a total of 3,387, which roughly equates to the approximately 3,054 additional sales attributable to the reinvigorated right to buy in 2012-13. To meet the target of replacing the roughly 8,512 homes sold in 2014-15 by the end of 2017-18, however, would require quarterly housing starts to reach around 2,130, a five-fold increase on recent figures of approximately 420 per quarter."
Replacement homes that would be sold under the scheme would not necessarily need to be "like-for-like", the NAO added, saying the properties could be "a different size, and built in a different area, compared to those that have been sold".