There are concerns the plans could undermine the NHS

The health directive was due to have been unveiled on Wednesday.

The EU said the move was purely for "agenda reasons", but the BBC has been told more work needed to be done "on the detail".

The UK government said it would fight for the right for the NHS to decide what treatment it will fund.

Critics of the scheme fear a two-tier service, with only people who can afford to travel taking advantage of the system.

We think it is critical.. that the NHS retains the ability to decide what care it will fund to meet the needs of individual patients Department of Health Health care across Europe Hard road ahead for reforms

Under the draft plans - which are now expected to be announced in the New Year - a patient would have to be referred by a medical professional and demonstrate they faced an "undue" delay for treatment in their own country.

They would have to pay for the cost of their treatment up front, and then claim it back from the NHS. The patient would also have to meet travel costs themselves.

'Two-tier' service

The proposals were drawn up in part as a response to the case of Yvonne Watts, who had a hip operation carried out in France.

The High Court ruled the NHS should pay for treatment abroad if patients had to wait too long.

The proposals will be subject to amendments and change by MEPs and ministers from member states, and may take several years to become law in the UK.

Former health secretary, Frank Dobson, warned that it would be the beginning of a two-tier health service.

He said: "This directive would mean that we would be implementing, in this country, the Tory policy of giving privileges to the well off and well informed, which was rejected at the last general election."

Dr Vivienne Nathanson, head of science at the British Medical Association, agreed that the proposals could potentially damage the health service.

She said: "If people started travelling for operations that are carried out very rarely there would not be enough need for that operation left in the UK, and the people who could not travel might find it extremely difficult to get that treatment."

'Stalking horse'

Dr Nathanson also warned that the system would have to be carefully thought through before implementation. She was concerned that UK doctors would be left to pick up the pieces if things went wrong abroad.

Nigel Edwards, of the NHS Confederation, said the proposals could make it hard to run an equitable system.

"There is a bit of concern that some of the advocates of free markets in the European Union, who have failed to infiltrate their ideas into health up to now, are using this as a bit of a stalking horse to try to create a much more US-style free market."

A Department of Health spokesman said: "We think it is critical that the legislative framework ensures that the NHS retains the ability to decide what care it will fund to meet the needs of individual patients."

Spain and Germany are also likely to oppose some of the plans.

However, Andrew Lansley, the Shadow Health Secretary, said: "These new proposals will not conflict with the principles of the NHS.