MEP Baroness Emma Nicholson, speaking on the BBC's Panorama, said this influx was leaching vital money away from the health service.

Baroness Nicholson has condemned private hospitals

The programme, to be screened on Monday on BBC1, also raises fears about the standard of intensive care at those private hospitals which do have intensive care facilities.

Baroness Nicholson's husband, Booker Prize chairman Sir Michael Caine, died following treatment at the King Edward VII Hospital for Officers, the London hospital used by members of the Royal Family including the Queen Mother.

Sir Michael went into a coma after a tube which was allowing him to breathe became blocked and nurses were unable to clear it. He died five weeks later.

Leading intensive care specialist Dr Carl Waldmann said that the chances of death would have been "minimal" had staff at the hospital been properly trained.

Dr Waldmann, a council member of the Intensive Care Society, told Panorama: "Here we are in the middle of London with a very prestigious hospital, and if it was unable to meet the requirements of a baseline intensive care unit, it should have made other arrangements."

However, the hospital has hit back, accusing Baroness Nicholson of orchestrating a "disingenuous... campaign of vilification" against it.

Chief executive Colin Harrisson said more than half of the hospitals intensive care nurses had formal specialist qualifications.

He added that the hospital had a higher nurse to patient ratio than NHS centres.

Transfers

But Dr Waldemann thinks Mr Caine would have been better treated by the NHS.

A survey by the Intensive Care Society found that over 500 patients are being transferred from private hospitals into NHS intensive care units each year.

Each bed costs the health service at least £1,500 a day to run.

Dr Waldmann said: "I and all other intensive care doctors are livid. The insurance companies would only have to be responsible financially occasionally, it would be a very small percentage of their turnover and it really would help us keep extra beds open."

Baroness Nicholson is scathing: "I find it repugnant that NHS beds should be used as a final resource by the private hospitals who set themselves up as being able to cope and yet demonstrably cannot.

"I don't see why the NHS resource should be leached away in this way."

But the insurers are adamant that the state should continue to pay for private patients who become so ill they have to be moved.

Dr Andrew Vallance-Owen, from BUPA, told the BBC: "Money shouldn't be coming into the argument at a time when your life is at risk.

"People who live in this country have paid their taxes and are entitled to use the NHS when their lives are at risk, and this is the one situation where we feel most strongly there is a principle involved."

Both doctors' organisations and House of Commons' Health Select Committee have called for extra regulation of the private sector to ensure the highest standards.