The cost of pension promises to 3.25m public ­sector workers is about £15bn ($27bn) more each year than government admits, even after recent cuts in benefits for new members and increased contributions for some other workers, according to a new study.

The findings, contained in a report to be released on Monday by John Ralfe, an independent pensions consultant, is based on an analysis of the annual accounts of the National Health Service, teachers, civil service and other public sector pension bodies.