The University and College Union is currently mounting industrial action over USS changes, which include a cap on inflation-proofing, a higher normal pension age of 65, and the replacement of final-salary pensions with career-average ones for new members.

The Employers Pensions Forum, which put forward plans for change on behalf of universities, describes rising longevity as the primary reason the changes are needed. But Tom Pike, a reader in microengineering at Imperial College London, said this "not only misleads staff as to the basis of any concern but ignores the much higher risks to the health of the fund that might result from USS investment strategy".

Tom Merchant, chief executive of the ?32.4 billion scheme, had a total remuneration of ?311,000 in 2010-11, while 13 USS staff were paid more than ?200,000 - up from eight the previous year.

Dr Pike plotted the funding level of the USS - the extent to which its assets cover its liabilities - against the value of the FTSE 100 index since 2002. He found the correlation was "startling".

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The fund's historically high proportion of investment in equities "meant it was only to be expected that USS is essentially a high-risk tracker fund, shadowing the price of shares".

But Roger Gray, chief investment officer at USS, said that lowering the fund's exposure to "return-seeking assets such as listed equities" means the "expected costs of providing future benefits will rise".

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"Therefore a balance needs to be struck between a strategy which avoids volatility in the funding of the scheme whilst ensuring that the cost of providing future benefits does not become prohibitive," he added.

However, Mr Gray said there had already been some changes in the USS, with the "strategic allocation to listed equities" reduced from 72 per cent of scheme assets to 55 per cent.

But Dr Pike said that the USS was now "locking in the losses into poorly returning fixed-rate assets from its 'massive equity bet' of the past decade".

Mr Gray also highlighted the "cumulative effect" of low equity market returns, historic lows for government bond yields and rising longevity.

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john.morgan@tsleducation.com.