It is one of the most common dilemmas of NHS financial management. The trust sets an annual expenditure budget. A budget holder underspends - no doubt for excellent reasons - and wants to carry the unspent balance forward into the following financial year.

Should the carry forward be allowed?

Say no, and human nature dictates that the budget in question will be fully spent in future years. Once bitten, twice shy.

But accommodating the carry forward may only be practicable if there are offsetting underspends elsewhere in the trust, as well as a degree of whole system flexibility not normally associated with public sector accounting.

The same issues apply at cross-government level. And, times being hard, the 2010 spending review announced a change in the rules, with “around £20bn” of accumulated surpluses from across government departments being abolished at the end of this financial year.

Gone. Just like that. There went £5.5bn of NHS underspends, quicker than a dodgy investment in an Icelandic bank. Now you see it, now you don’t.

Of that “around £20bn”, £3.71bn was the accumulated NHS revenue surplus, the product of three years of cost improvement and demand management schemes.

Another £1.76bn was NHS capital that won’t now be available to maintain and improve the estate.

In previous years the Department of Health has deftly juggled surpluses, deficits and slippage within the NHS and ensured that organisational carry forwards can be honoured.

But that was in times of growth. Now, with huge savings to make and huge restructuring costs in prospect, the financial buffer so carefully amassed has been snatched away.

The DH will do its best to honour surpluses, but may struggle. There are hints that the pace and timing of funding may suffer. Besides, of the £3.71bn, around £1bn consists of foundation trust accumulated surpluses to the end of 2009-10.

Foundation trusts, which in general have little use for Richmond House, will probably be rather keen to have them back. Will their surpluses take priority over the rest of the NHS? If not, and it emerges that foundation resources have also evaporated, their regulator Monitor will be sorely displeased.

Noel Plumridge is an independent consultant and former NHS finance director,