Four out of five first-time homebuyers under the age of 30 are calling on the “Bank of Mum and Dad” to raise deposits that now average nearly £36,000, according to the Council of Mortgage Lenders.

Meantime, Nationwide reported that it has received only “a handful” of inquiries for a package introduced on June 10, intended to help existing customers in negative equity to move home. Not a single deal has yet been completed, a spokesman for the building society said.

In an extreme case this plan could leave borrowers with loans of up to 125 per cent of the value of their new homes - but only after they have put up a five per cent cash deposit.

“The actual value of the negative equity and the loan to value will reduce in all circumstances,” Nationwide insisted.

The CML said that the number of mortgages to first-timers crept up to 14,000 in May from 13,700 in April, but 29 per cent fewer than in May last year.

Tough standards set by banks and building societies enabled first-timers to borrow an average of only 75 per cent of the cost of their homes – against 89 per cent last May.

The CML calculates from earlier research that 80 per cent of this year’s young first-timers are being helped by their parents or other relatives. In 2007, when 95 per cent mortgages were widely available, the proportion was 40 per cent.

Recently, though, some mortgage lenders have devised financial products to link parents’ savings with their sons’ or daughters’ house purchase.

A CML spokeswoman said there was no sign of parents re-mortgaging their homes to raise a deposit from their children, though some might use cash released when they trade down to a cheaper home.

Overall, banks and building societies lent 37,400 mortgages for house purchase in May. Over the last seven years, they lent an average of 96,000 house purchase mortgages in the month of May.

Demand for re-mortgages is sinking fast as borrowers with fixed-rate deals coming to an end find they can revert to attractive standard variable rates with their existing lenders.

Some, too, are trapped by falling house prices, which do not leave them enough financial headroom to qualify for an attractive re-mortgage, even if they are not in negative equity.

Home movers accounted for 23,500 of May’s mortgages, five per cent more than in April and 27 per cent fewer than in May last year. For a second month, their loans averaged 67 per cent of the value of their homes, and 2.68 times their annual incomes. The CML noted that lenders have stopped tightening their terms.

Mortgage interest took 11.3 per cent of home movers’ incomes in both April and May, against 17.1 per cent in May last year.

The cost for first-time buyers was 14.9 per cent of income, down from 19.7 per cent a year earlier.

Paul Samter, a CML economist, commented: “The trend of tightening lending criteria seems to have subsided and we may see a modest easing in these measures over the summer, which will be some help to borrowers.

“But overall, access to mortgage finance will still be constrained by the diminished number of active lenders and shortage of funding available to them.”