We live in strange times when we have to depend on private medicine to bail out a health service which is revered by the British people

Dr Ian Gibson MP

Mr Milburn rejected suggestions that the move was "privatisation by the back door", insisting it simply allowed NHS patients to be treated more quickly.

But David Hinchliffe MP, the Labour chairman of the Commons health select committee, immediately said the concordat was "wrong".

And Labour backbencher Tony Benn described it as a step towards privatisation of the NHS. "This is a very serious move," he said. "It is the privatisation of the NHS."

"The NHS is run down for lack of money, so you bring in the private sector. Once you have done that, why not make it all private?

"Why are there not enough resources for the NHS? Because the government has promised high earners that it will not increase their income tax.

'Very wary'

Peter Kilfoyle: "A step in a direction I don't want to go"

Other Labour backbenchers soon joined in expressing deep unease at the government's move.

Dr Ian Gibson MP told BBC News Online: "We live in strange times when we have to depend on private medicine to bail out a health service which is revered by the British people.

"You can't on the one hand condemn private hospitals for abusing the NHS by utilising our trained staff and services and then attempt to pretend that it supports the NHS."

Former defence minister Peter Kilfoyle echoed the concerns, saying: "I share that unease and feel very wary indeed about what's proposed. I can understand a short-term palliative measure but I'm concerned about a number of things."

The concordat was "a step in a direction I don't want to go, in marrying the two sectors".

I have grave concerns at this development

Jeremy Corbyn MP

"There's quite a difference between a health service for profit and one free at the point of need. I also wonder if inadvertently we may be being used to bail out a private sector that needs more money."

He said he would be seeking an opportunity in the Commons to get "categorical assurances that the deal is a one-off short term palliative and is not in any way going to become some regular feature".

'Grave concerns'

Islington North MP Jeremy Corbyn shared Mr Kilfoyle's fears. "I have grave concerns at this development," he said, saying he hoped it was "not the start of the creeping privatisation of our national health service".

"Public funds ear-marked for the NHS should not be used to boost the private sector which will readily expand to meet any extra demand."

Fellow Labour MP Lynne Jones said she supported Mr Milburn's deal with the independent sector - but only as an emergency short-term move.

"So long as it is only a temporary measure while the NHS is building up capacity, I am not opposed," she said. "But I would be very worried if it were any more than an interim measure."

Her view was backed by Dr Howard Stoate, a Labour member of the health select committee. "I have reservations but it would be crazy to have spare capacity free when there are people in need," he said.

He said Mr Milburn was taking the right step "while the NHS is being restored to what I would like to see as its proper self-supporting role, but anything more than a short-term measure would be unacceptable".

Mr Milburn's announcement of the concordat came the day after Labour launched a trenchant attack on Conservative tax plans as tantamount to privatising the health service.

Government sources described the concordat as "breaching the ideological barricades" to using private sector resources.