The former head of the civil service has attacked plans to extend the right-to-buy to housing association properties as "wrong in principle and wrong in practice".
Under proposals included in the Conservative manifesto, housing association tenants will be given discounts of up to £104,000 in London and more than £77,000 elsewhere if they choose to buy their properties.
The government says housing associations – which are independent charities – will be compensated for the discounts through funds raised by forcing local authorities to sell off their most expensive vacant properties. Ministers claim that this will ensure a "one-for-one" replacement of any affordable properties sold.
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But Lord Kerslake – head of the civil service between 2012 and 2014 and also permanent secretary of the Department for Communities and Local Government until earlier this year – this morning questioned the figures put forward by the government, and warned the plans could put further pressure on housing supply.
"I personally doubt the numbers – we need to see them," he told the Today programme.
"But I think more importantly the capacity to rebuild is highly doubtful. If you look at the current policy on one-for-one replacement by local authorities, in fact for every 10 houses sold only one new house is being rebuilt and I think with this policy the rate would be even less good."
The crossbench peer, who is now the chair of the Peabody housing association, also rejected claims that housing associations who had raised concerns about the policy were motivated by self interest.
"I think housing associations have been highly adaptable and they have been a critical part of delivering new housing in this country," he said.
"Something like a third, occasionally up to a half, of the new houses have come from housing associations. They have also been very innovative in bringing in new products – so shared ownership as a way of allowing people to own their property. So I don't think this is about a resistance to change, it's a fundamentally wrong-headed policy."
He added: "The route to greater home ownership, which I'm actually very much in favour of, is to build more houses and that needs collaboration between housing associations, house builders and government, and it's likely that this policy, I think, will push that backwards rather than forwards."
Lord Kerslake will raise his concern over the plan – which has also been attacked by the CBI business lobby group and the Chartered Institute of Housing – in the House of Lords tomorrow as peers continue to debate last week's Queen's Speech.