Watson Wyatt, a firm of consultants to more than half of the country's biggest schemes, told the Times that three years of stock market falls had left a �70 bn black hole in pension funds.

As a result, more final salary schemes - traditionally seen as the best type of pension - could be closed to new entrants or even wound up by employers.

Roger Unwin, head of investment at Watson Wyatt, urged pension schemes to invest in property and ultra-safe bonds rather than shares.