Chancellor Gordon Brown yesterday outlined plans to help up to 100,000 first-time buyers on to the housing ladder with a part-ownership scheme.

Couples will have to raise as little as half the cost of homes sold on the open market under a deal struck between the Government and mortgage lenders.

The rest of the equity in the property would be shared between the Government and the bank or building society, potentially cutting average repayments on a £200,000 home by up to £372 a month.

The scheme received a broad welcome from lenders. But it also prompted a warning that unless it went hand in hand with an increase in housing supply, it would risk fuelling price rises.

A spokesman for the Halifax said: "The housing market depends on first-time buyers, they are almost its heartbeat.

"We need them to keep it healthy. Without them it slows down, so initiatives like this are very, very good."

Sue Anderson, of the Council of Mortgage Lenders, which has been involved in the scheme's development, said it was a very positive step, but she added: "We've got to see more housing supply accompanying this, otherwise there's the risk that all you do is push up house prices further."

The scheme will not be restricted to key public sector workers previously helped by the Government, and there will be no means test.

"However, banks and building societies will have to sift out deserving applicants whose salaries do not stretch to the average-priced house, from those wanting to buy dream homes beyond their means.

Interviewed on BBC 1's Breakfast with Frost programme yesterday, Mr Brown, who will unveil details of the initiative on Wednesday, said he believed shared equity schemes would help up to 100,000 people over the course of the Parliament.

Under the plans, the buyers would need to raise mortgages ranging from 50 per cent to 75 per cent of the cost of the property. The rest of the equity would be divided between the Government, the lender or possibly the house-building company.

Buyers would pay a nominal "rent" of no more than three per cent on the part they do not own, with the option to buy the whole stake if their fortunes improve.

The scheme, which would be run by the Office of the Deputy Prime Minister in partnership with local housing associations, would focus on new-build properties.

A Treasury source said although there would be upfront costs, it was essentially a form of investment.

Theoretically, if the value of a property declined after it was bought, it would be the Government's stake that would bear the brunt of the loss. In the more likely event that the property's value increased, the Government would be entitled to a percentage of the profit.