Gordon Brown said the Government would be making £200m available to buy newly-built homes that could not be sold on the open market, and would then rent them out to social tenants.

And he announced plans to expand a scheme for first-time homebuyers, allowing individuals and families with household incomes of below £60,000 to join shared-equity schemes previously only open to key public sector workers.

But property experts warned that such schemes – which help buyers to acquire part of a property's value and pay rent on the remainder – would still be affected by a downturn in the housing market.

David Holmes from Yorkshire Building Society said shared equity schemes were "no magic wand" and buyers could still find themselves with negative equity if the housing market slumps.

"There's no magic wand even in shared equity schemes. If you are particularly concerned about what's happening in the housing market, maybe it's a good time to wait until prices come back," he said.

But he added shared equity schemes could help people who were "nesting" and intended to stay in their house for longer, and not speculating.

Housing charity Shelter warned the measures were just "a drop in the ocean" when trying to tackle the housing crisis.

Housing Minister and Don Valley MP Caroline Flint said: "Most families aspire to get onto the housing ladder, but are being priced out of the market. We want to give them the support to help them buy an affordable home.

"The long-term solution to the challenge of affordability is to build more homes. But in the meantime, we are doing more by giving more first time buyers the chance to boost their purchasing power and put their dream home within reach."

The National House-Building Council welcomed the move. Chief executive Imtiaz Farookhi said: "We welcome the additional support for first-time buyers which will help ease some of the current market pressures and look forward to further details.

"NHBC will use its unique position working closely with industry, government and consumers to help meet the housing challenges ahead."

The Chartered Institute of Housing said it was important first-time buyers were given good advice before buying.

Chief executive Sarah Webb said: "While the announcement that shared equity schemes will be extended is also welcome, we need to ensure that good advice is available to minimise the risk to people wanting to take up the schemes.

"We also need to think more creatively about putting in place a flexible equity scheme to help vulnerable home owners."

Questions were also raised last night on whether the £200m promised to buy newly-built homes that developers could not sell was being brought in to save Gordon Brown's pledge of three million new homes by 2020 from disintegrating.

Developers have said they were reluctant to build the homes in the current climate – and there were speculation last night the money had been promised by the Government as an insurance policy to keep houses being built and saving the Prime Minister from looking weak.

It was also pointed out, with an average house price of £150,000, the £200m being made available would only pay for 1,300 homes.

Gordon Brown also announced yesterday plans for a Banking Bill which would "underpin Britain's banking system with the best protection for depositors".

A Savings Bill will help homeownership and wealth ownership by giving eight million people on low income access to a national savings scheme, with each pound saved matched by a contribution from the Government.

And, as announced in the Budget in March, the Government will take forward plans to give each department a specific annual limit on how much new regulation each is allowed to impose.