Standard Life is taking a £37 million hit on its first-quarter profits to underpin guarantees made to investors in one of its global liquidity funds that they can get back the original cost of their investments.
At the same time it is restructuring the fund and withdrawing that guarantee for the future, and substituting a formula linking investors' entitlements to the "mark to market" value of the funds' underlying investments - high-yielding asset-backed securities, many based on mortgages.
Some of these are now being replaced with corporate bonds.
Similar problems with low "mark to market" valuations of investment packages for which the market has virtually dried up lie behind many of the far bigger write-downs forced on British and American banks.
Standard Life said it expects the cash cost to be no more than £17 million after tax because many of the underlying securities will deliver their full value when they mature.
A spokesman also said that most organisations who invest in the fund for a high-yield on money they can withdraw at seven days' notice will have to accept the new, more limited, guarantee.
Local authorities may be an exception, he added.
In a separate move to lower risks to its shareholders, Standard Life has reinsured £6.7 billion of liabilities to pay life-time pensions to owners of its annuities.
It believes this is the biggest UK deal of its kind, lowering the risk of these pensioners living longer than expected.
Standard Life reported worldwide life and pensions sales up eight per cent in the first quarter of this year at £4.47 billion on the basis of the present value of new business premiums.
The UK accounted for £3.51 billion of that, a six per cent increase.
Using a new measure setting claims, maturities and surrenders of its policies against new sales, Standard said its net inflows were up 31per cent to £986 million worldwide and by 42 percent to £826 million in the UK.
"We have delivered a solid performance in the first quarter against a backdrop of economic uncertainty and volatile markets," said Sandy Crombie, chief executive.
"While market conditions ahead appear challenging, particularly in the UK, we remain confident in our ability to outperform in the profitable segments in which we operate."
Like other mortgage lenders, Standard Life has cut back its new lending sharply to drive profitability in difficult credit markets.
Only 0.22 per cent of its existing mortgages are in arrears, it added, against an overall average of 1.2 per cent reported by the Council of Mortgage Lenders.