UK - Small assumptions on things such as inflation, investment returns and life expectancy are having a big and varied impact on the UK's largest pension funds.

According to Mercer's latest pension accounting assumptions survey, FTSE100 company pension schemes have increased their longevity assumptions for their pensioners for the fourth year in a row, and that increase has in turn raised scheme liabilities by 1.5%.

The survey showed that FTSE100 companies, compared with the end of 2008, have increased their longevity assumptions by five months for current pensioners and as many as seven months for future retirees.

The report also highlighted "continuing disagreement" among the UK's largest companies on inflation assumptions - ranging from 3.1% to 3.9% per year - as well as the expected long-term rate of return on equities - ranging from 6.9% to 9.2% per year.

Warren Singer, UK head of pension accounting at Mercer, said accounting assumptions "really make a difference" when working out a given company's pension liabilities. 

"Rising life expectancy continues to have serious financial implications for pension schemes," he said.

"Overall, changes in accounting assumptions have increased the median FTSE100 company's UK pension liabilities by around 20%."

Singer said the wide range of views taken by companies on accounting assumptions made it very difficult for users of accounts to compare pension accounting disclosures.
"There is no single correct answer for these assumptions," he said.

"Therefore, the IASB (International Accounting Standards Board) is proposing to address the diversity of views by requiring additional disclosure information, such as the sensitivities of liabilities to assumption changes."

Mercer highlighted that the IASB has proposed replacing the accounting assumption for the expected rate of return on equities - the largest variation - with the yield on high-quality corporate bonds from 2013.

This proposal, the consultant said, will increase the "financing cost element of profit or loss for the vast majority" of the UK's top companies.