Hospitals in the South East are facing a growing cash crisis, according to a leaked letter.

The letter, sent from managers in the South East region of the NHS to hospitals and local health authorities, reveals that the area is facing an overspend of £60 million in the current financial year.

In the letter, seen by the BBC, the region's chief executive, Ruth Carnall, calls for drastic action to cut the deficit. Only key government targets on the length of time spent waiting for treatment or an ambulance are to be immune from the cost-cutting.

"I cannot overemphasise the seriousness of our financial position and the impact this has at a national level. Collectively we have to find solutions in a very short time-frame, and I need all your commitment to delivering this," she writes.

Describing how she had until the end of this week to explain to NHS chiefs how the money is to be saved, she said: "I do not want reasons as to why savings cannot be achieved, but proposals as to what savings can be actioned. I recognise that this will mean reductions in areas that do not contribute to national imperatives."

Health secretary Alan Milburn said the money £60 million represented just one per cent of the region's yearly spending, and promised the shortfall would not affect patient care.

"The NHS is spending around £1 billion a week. Within that sort of considerable sum of money there is always some slack available for difficult circumstances," he told Radio Four's Today programme.

"There will not be an adverse impact on patient care, because the south east region will get loans from other parts of the NHS precisely to deal with this. I have asked Nigel Crisp to ensure that...an adverse impact on health care doesn't happen at all," said the health secretary.

But the Conservatives said the government was putting accountancy before the needs of patients.

Shadow health secretary Liam Fox said the letter epitomised how the NHS was being run. "First of all, it is very centralised with civil servants in Whitehall telling those on the ground what to do. Secondly, there is an accountancy-first procedure, which seems to put patients' interests second and seek to preserve the government's targets at all costs."

And he warned: "It is going to mean cuts in patient services. I can't see how it can be done otherwise."