The union said the report goes a long way to debunk the mistruths often perpetuated about the affordability of public sector pensions.

Prospect Pensions Officer Neil Walsh said: “By presenting the figures in terms of an annual percentage of Gross Domestic Product the NAO have brought clarity to a issue which other partisan groups often seek to bury in alarming multi-billion pound liability figures.

“The report makes it clear that public sector pensions are far from being the unsustainable burden on current or future generations of taxpayers they are often portrayed as.

“Rather, when viewed in terms of percentage of GDP and thereby an indication of the country’s ability to pay, projected costs look set to rise from 1.7% of GDP today to a peak of 1.9% in 18-19 years’ time and then back down to 1.7% by 2059-60.

“This doesn’t even allow for all the effects of the public sector reforms agreed in 2007 which have had the desired effect of limiting future taxpayers' liabilities.”

Walsh said the report, The Cost of Public Service Pensions, also demonstrated that attempts to stir up a culture of envy with claims that they are overgenerous fall far short of the facts.

“Not only do the figures show the average civil service pension is under £6,000pa but that members of these schemes are paying more for the benefits – the average civil servant contribution is 59% higher than 10 years ago.”