Forcing the sale of high-value council properties in order to subsidise the right to buy for housing association tenants is unfair, the Lords heard.

Liberal Democrat peer Baroness Bakewell of Hardington Mandeville warned that larger families could be broken up or made homeless by the onus on local authorities to dispose of bigger dwellings in order to fund a levy for housing association tenants to get a better deal when buying their homes.

With only some of the money raised earmarked for replacement council housing which does not have to match the size of properties sold off, opposition peers said the Government was adding to the housing crisis.

Lady Bakewell accused ministers of acting like "Robin Hood in reverse" as the Lords debated the committee stage of the Housing and Planning Bill.

"It seems extreme folly to force councils to sell off the one asset that allows people to remain in their homes," the peer said.

Lady Bakewell warned making local authorities sell high-value properties would mean much less larger scale accommodation would be available to families who may be bigger than normal due to cultural or religious reasons.

"The Government should not be discriminating against these families just because they are large. This could lead to increased homelessness or families being separated," the Lib Dem said.

Crossbench peer Lord Kerslake urged a rethink on the policy as he accused the Government of pursuing "manifesto fundamentalism" over the issue.

"These most definitely are not surplus properties. They may be vacant but there is a massive demand to take up the vacant properties," Lord Kerslake said.

Fellow crossbench peer Lord Best said: "This taxing of councils to give discounts to housing association tenants is extraordinarily unhelpful."

Tory former cabinet minister Lord Young of Cookham defended the Government action, insisting it would "recycle" affordable housing as the proceeds from council sales would give discounts to housing association tenants, or be used to redevelop brown field sites.

"This is recycling assets in order to increase supply. This is about stimulating building," Lord Young said.

Communities and local government minister Baroness Williams of Trafford defended the Government's policy, insisting it was a "flagship manifesto commitment".

She said the market value of local authority housing stock in 2014 was over £200 billion. By requiring councils to sell high-value homes as they fell vacant , the "locked-up" value could be used to build new homes and extend home ownership.

Lady Williams said the agreements process would give local authorities more freedom to build replacement homes that met their communities' needs.

"Local authorities will be able to decide on the tenure of the homes and where to build them."

She warned against putting "unnecessary hurdles" in the way of enabling housing association tenants to buy their homes and building new homes the "country so desperately needs".

Labour's spokesman, Lord Beecham, hit out at the policy and demanded that the total number of high-value properties to be sold off should be limited to no more than 10% of total local authority stock in a particular area - "capping the impact" of the scheme.

He said: "This concept born of at best ill-conceived populism and at worst electoral opportunism is about buying votes, not building houses.

"It is a shoddy, ill-thought-out, ill-drafted piece of legislation. We are asked to approve it in the absence of evidence of how it will work and what its impact will be."

Lord Beecham urged ministers to take the plan back to the drawing board and think again.

Later the minister faced fierce cross-party protests when she disclosed that some of the details of the policy would not be available until after the Bill had become law.

Labour former minister Baroness Hollis of Heigham said it was wrong not to have details on the apportionment of money between replacing local authority housing and paying housing association discounts.

"We can't make legislation on this basis when all the detail is in the ether," she said. "This is a travesty of House of Lords procedure."

As Liberal Democrat peers joined with the objections and Labour called for the Bill's consideration to be "paused," Lord Beecham said the minister had been placed in an impossible position.

"The House has confidence in her but no confidence in the way the Government has proceeded with this Bill," he added.

Lady Williams assured peers that much of what they had said in the debate would be used to "inform how the regulations will be shaped".