Adair Turner's interim report on Tuesday should range across many aspects of the pensions crisis. I expect the Pensions Commission chairman will touch on the increasingly important issue of longevity risk. This issue lies behind the widespread belief that annuity returns have fallen. It is also at the heart of some of the problems that occur when pension funds wind up.

If, as expected, Turner & Newall, the insolvent automotive parts manufacturer, folds its pension scheme, its trustees will be obliged to use their assets to purchase annuities for current pensioners and deferred annuities for members of the scheme who have not yet retired. At that moment, one of the strangest features of the British pension scene will be revealed. There are only two companies that still sell deferred annuities in bulk - Prudential and Legal & General. Both have tight limits on how many they will sell. The trustees could find themselves required by law to buy something which cannot be supplied. How could we have got ourselves into this position?