Chancellor Gordon Brown yesterday outlined plans to help up to 100,000 first-time buyers onto 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.

The Halifax welcomed the scheme as ''very, very good''.

''The housing market depends on first-time buyers, they are almost its heartbeat,'' a spokesman said.

''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 yesterday's BBC 1's Breakfast with Frost programme, Mr Brown said he believed shared equity schemes would help up to 100,000 people over the course of the Parliament.

Mr Brown, who will unveil details of the initiative on Wednesday, told the programme the Government was moving on to the next stage of its economic policy.

''We have created stability in this country, and now we must ensure that the benefits go particularly to young couples who want to own their own homes, who find that house prices have been high, who could benefit from low interest rates, but they need some help to get on to the first rung of the housing ladder,'' he said.

The move comes amid signs of a gradual slowdown in the housing market.

If new buyers cannot enter the market, selling chains could eventually grind to a halt, potentially undermining the rising property market, which in recent years has helped to keep consumer demand and the wider economy buoyant.

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 stressed that although there would be upfront costs, it was essentially a form of investment.

Theoretically, if the value of a property declined after it was purchased, it would be the Government's stake which 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.