He also wrote to the National Audit Office (NAO) – the watchdog responsible for certifying the accounts of all government departments – asking it to investigate Right to Buy.

Healey questioned Lewis about the cost to the public purse of plans to extend Right to Buy to housing association tenants.

Lewis didn’t give figures in his response. He said: “The details will be set out in the impact assessment when the Housing Bill is published, but it is all about ensuring that we support people who aspire to own their own home and extend home ownership to as wide a group of people who wish to have it as possible, and on equal terms to those who have had it for so many years.”

Healey described Lewis’ response as “a load of waffle”.

“It is quite clear that the minister has made no assessment at all of the costs of the policy. When he produces the impact assessment before the bill is published and brought before the house, will he ensure that it shows that taxpayers will pay three times over: first, for the investment to build the homes; secondly, for the discount to sell them; and, thirdly, for the higher housing benefit bills that will result?” said Healey.

In a letter dated 29 June to NAO controller Sir Amyas Morse, Healey outlined his concerns and said the policy “risks becoming a severe failure of ministers to achieve value for money in public spending”.

Healey described government plans to extend Right to Buy to housing association tenants as “bad for the public purse and bad for the taxpayer” and warned it would push up the housing benefit bill as many homes sold under the policy end up being let privately.

Healey claimed his analysis of government figures showed that the Right to Buy units lost in this Parliament alone could add £1.5bn to the housing benefit bill over 30 years and will cost taxpayers three times over.