The pension funds of the FTSE 100 companies currently have a deficit of £41bn, according to research by actuarial group Lane Clark & Peacock (LCP).

The data represents the biggest annual swing in funding since 2002, with the same companies enjoying a £12bn surplus in July 2007.

"No sooner have companies breathed a sigh of relief about returning to surplus than they are back to multi-billion pound deficits," said Bob Scott, a partner at LCP.

"With a possible recession looming and the threat of further regulatory intervention, the outlook for continuing defined benefit provision seems rather bleak."

But the results could have been far worse, he added, praising efforts made by many organisations to reduce the risk and deficit.

Companies have put nearly £40bn of their own revenues into the schemes in the last three years.