The NHS year-end surplus may not be quite as easy to predict as you might think.

This month the Department of Health estimated a stash for 2008-09 of£1.75bn. But two pressures have emerged which may complicate the sums.

First, some primary care trusts are being pushed into deficit by a sharp rise in GP referrals to acute services.

Cloudy forecast

Second, if a letter about wrapping up the 2007-08 accounts from NHS London is anything to go by, trusts and PCTs are becoming extraordinarily diligent at ensuring every possible cost is accounted for. Those in the capital are being egged on by a handy list of 21 suggestions for tightening up their numbers.

This does not, of course, amount to creative accounting. It is, after all, well known in NHS accountancy circles that capitalisation of hearing aids is a pressing issue.

But it does mean that see-sawing spending and something approaching a pick-and-mix approach to accounting - depending on whether a PCT needs to get its numbers up or down - clouds the financial crystal ball.