Mortgage payments are making up the biggest share of take-home pay for 17 years, according to figures released today.

The affordability gap has grown because property prices have risen three times faster than salaries in the past decade. Homeowners are spending a bigger proportion of their salary on the mortgage than at any time since the summer of 1990, according to a bleak assessment by the Royal Institution of Chartered Surveyors (RICS).

First-time buyers must spend almost five times more than they did a decade ago to get on the housing ladder, with poorer families having to save almost a year’s salary for stamp duty and a deposit.

The survey comes before tomorrow’s meeting of the Bank of England, which is expected to put a further rise in interest rates on hold. The Bank has already raised rates five times in the past year.

The new data raises the prospect of a surge in home repossessions, puts pressure on Gordon Brown and has prompted attacks from both Left and Right. The Conservatives say that Labour’s increases in stamp duty have hit first-time buyers hard.

The Prime Minister made housing an early priority, announcing plans to build three million homes by 2020, with up to 70,000 new properties a year to be designated as social homes for key workers and low-income families.

David Stubbs, the RICS senior economist, said: “First-time buyers are facing an enormous struggle to access the housing market. This may worsen if the turmoil in the US market forces mortgage providers to tighten lending criteria and demand even higher deposits.”

But he added that pressures may be nearing their peak, with house-price growth expected to be below earnings growth in 2008, while interest rates may also start to fall during the second half of next year.

Grant Shapps, the Shadow Housing Minister, said: “Despite all Gordon Brown’s rhetoric, it is now more difficult than ever to get on the housing ladder. Labour ministers have made life harder for those trying to buy a property, with additional costs like stamp duty which now hits first-time buyers.

“These figures demonstrate that, after ten years, this Labour Government has made the dream of homeownership more distant than ever for millions of people.”

The study found large regional variations, with London the most difficult place for low-earning couples to get on to the property ladder, followed by the South East and the South West.

In all of these regions couples on low earnings would have to save more than their combined annual take-home pay to afford a deposit and the stamp duty.

Research from Abbey, the high street bank, showed that first-time buyers in the South borrow nearly a third more than those in the North. People buying their first home in the South now borrow an average of £128,370 — 31 per cent more than the £89,189 that first-time buyers in the North borrow.

The gap between pay and house prices has grown most in West Sussex, where prices have gone up more than nine times faster than salaries, followed by Waltham Forest, in East London and Luton, in Bedfordshire, according to the RICS study. In Kensington and Chelsea, in Central London, the average property price of £500,000 is almost 20 times the local average annual salary of £26,000.

Across London, couples in the bottom quarter of earners are now having to spend 51 per cent of their post-tax income on their mortgages, compared with 33 per cent for couples in Yorkshire and Humberside.

Brendan Barber, General Secretary of the TUC, called on the Government to take action. “These stark figures bring alive the housing crisis,” he said. “They show just how quickly buying your own home has gone out of the reach of many working people.

“It is striking that house prices seem to have gone up in line with the pay of top directors and the super-rich, rather than middle and low earners.”

Yvette Cooper, the Housing Minister, last night admitted that the Government had more to do. “This report shows how important it is for councils, communities and house-builders to back plans for two million more homes by 2016.

“The long-term rate of housebuilding has not kept up with rising demand, causing long-term house prices to increase. The level of new housebuilding is at its highest since 1990, but we need a national consensus on building more homes.

“Those who are still opposing new homes need to face up to the unfair consequences for first-time buyers and young families who badly need new affordable homes.”