BP, one of the last remaining FTSE 100 companies to offer final salary pensions to new workers, said it would shut that window from next April so as not to burden shareholders with unknowable risks and costs.

“We are doing this to avoid burgeoning future liabilities,” a spokesman said, adding that BP is most concerned about the sharp and unexpected rise in life expectancy at older ages which has dramatically increased costs. “It is a big financial burden to leave to shareholders,” he said.