When the going gets tough, the tough hide their surpluses from the grasping claws of the strategic health authority.

At least, that is what Monitor’s as yet unpublished review of the last quarter of 2010-11 suggests.

As ever, the review shows foundation trusts sucked in more income than planned in 2010-11: £588m extra of it.

But elsewhere we find there was at least another £183m of cash foundation trusts received, but did not book as income for 2010-11, defining it instead as “pre-payments” for services they will provide in 2011-12.

All very right and proper: accounting rules state organisations should not record an expense until the good or service to which it relates is actually received or consumed, and vice versa for income.

A painful “agreement of balances” exercise takes place each year in which primary care trusts and health service providers attempt to ensure their books match up: that PCT X’s £105m of expenditure with NHS trust Y is mirrored in Y’s accounts.

At base, the exercise is a safeguard against fraud.

But it should also mean that if PCT X has a nice fat surplus left over from 2010-11, that would be apparent.

Even if the PCT has committed that surplus in the form of prepayments for 2011-12, those prepayments cannot be recorded as 2010-11 expenditure and the surplus would be there: like a big fat sitting duck, waiting for someone – the SHA, the cluster or the Department of Health – to come and pick it off.

But the beautiful loophole from the PCT finance director’s perspective is that foundation trusts do not have to take part in the agreement exercise.

That opens the door to PCTs booking an expense for one year, even if the foundation trust only books it as income the next.

It looks as though around 20 PCTs used the tactic to tuck away about £5m apiece at the end of March.

Given the lumpy distribution of past NHS surpluses and the growing list of worthy causes in need of bailing out, the practice suggests the few surplus-rich PCTs will not be prepared to share their wealth without a fight…

Sally Gainsbury is a news reporter for the Financial Times.