One of the hidden extra costs of foundation trust status is paying a bank for a “working capital arrangement”.

Such an arrangement is essential for preserving your financial ratings. Rather like an overdraft, it covers the risk of cash flow unexpectedly drying up.

Monitor determines how much money this arrangement should cover. One month’s expenditure is typical. If a foundation trust draws upon its working capital arrangement, it pays interest on commercial terms, perhaps a couple of percentage points above base rate.

But even if the arrangement is never used, the bank charges a fee. Last year the Foundation Trust Network estimated the total cost of working capital arrangements at over £20m per year, suggesting a bill for some FTs sufficiently premier league to buy a Cameron/Osborne dinner.

This is an extra cost arising from the competition “level playing field”. In the past, a struggling trust would borrow, temporarily, from within the NHS “family”.  But market freedoms come at a price. That £20m is real NHS money, quietly being hoovered up each year by the banking system.

For the banks it’s a nice little earner. The fees are rising: many have doubled in recent years. And better still, there’s an elegant catch. Any FT actually needing to use its working capital arrangement is almost certainly an FT heading for a breach of its terms of authorisation… and hence no longer entitled to a loan.

“There have been examples,” the Commons Treasury committee heard last year, “of FTs actually needing the cash, and finding the facilities withdrawn”.

Bankers were always known for lending you an umbrella when the sun shines, then wanting it back as soon as the rain begins.

But lack of working capital is a serious problem, with 4 per cent annual efficiency targets stretching to the distant horizon. Service reconfiguration requires cash.

However, cash is something foundation trusts have in plenty: £3.3bn of accumulated balances at the end of 2010-11. So why don’t FTs cooperate, finance their own working capital and cease reliance on this particular banking “service”? Or would that somehow miss the point?