There were more than 900 compulsory redundancies in the NHS in first half of this year, according to official figures that unions claim only represent a fraction of the total number of job losses in the health service.

The Department of Health statistics revealed that there were 903 redundancies in England between April and September 2006.

These included 167 clinical staff and 736 non-clinical workers. The worst-hit area was London, with 299 compulsory redundancies, followed by the West Midlands with 187.

The Royal College of Nursing, the nurses' union, said that the lost jobs were part of an estimated 20,000 reduction in the NHS workforce as a result of the deficit crisis hitting hospitals and trusts across the country.

"Ministers should be under no illusions about the serious impact on patients' care if these posts are lost to the NHS," said the RCN's general secretary, Beverly Malone.

A spokeswoman for Unison, the public services union, said that today's figures "were the thin end of the wedge".

She added: "We know that thousands more posts have been frozen and agency staff are no longer being used. It [the threat of redundancy] is hanging over health staff like the sword of Damocles."

Lord Warner, the minister for NHS delivery, said that the job losses should be seen in the context of a 300,000 increase in staff numbers since 1997, a rise of more than 29%.

"The figures we have published today show the true picture of redundancies in the NHS: just over 900, not the inflated figure some have claimed," he said.

"We have always said there will be a minority of redundancies, which is regrettable, but employers will do all they can to support those staff.

"In the main, employers are taking alternative steps to minimise the level of compulsory redundancies, such as reducing staff levels through natural turnover - which is around 130,000 staff every year in the NHS anyway - redeployment and by reducing demand for agency staff."

But Dr Malone said that the bulk of the 20,000 job losses identified by the RCN was made up of voluntary redundancies and posts which will be frozen or remain unfilled.

She said she was "dismayed" that ministers had failed to provide details of these job losses alongside the much smaller number of compulsory redundancies.

"A post lost - whether through redundancy or freezing and deleting posts - means there is a job not being done and a service not being given," warned Dr Malone.

Earlier this month, Tony Blair played on the public confusion between compulsory redundancies and the total reduction in the workforce at his month press conference.

When challenged on the issue, he said: "The actual numbers of compulsory redundancies - which is what most people would understand by job losses - as far as I can see from the figures I have got, is a few hundred, not 20,000."

When the Conservative leader, David Cameron, said last week at prime minister's question time that there were 20,000 job losses in the health service he was accused by a minister of scaremongering.

Commenting on today's figures, the Liberal Democrats' health spokesman, Steve Webb, said that the government was trying to "temper public concern" about the cuts in the NHS.

"If a post falls vacant and is not replaced then the NHS has one less doctor, nurse or support staff. Yet today's figures do not show this," he said.

"With most trusts still consulting on what form job losses will take, we are only seeing the tip of the iceberg."

The Department of Health also released a new framework for NHS trusts on dealing with "managing workforce challenges".

It advised that trust managers should give staff at risk of redundancy priority when filling vacancies and ensure that any who lose their jobs are offered interviews with personal careers advisers.

Meanwhile a report by Bupa, the private health insurers, said that the NHS could be heading for a £11bn funding gap by 2015.

Longer waiting lists and more staff cuts are likely unless the government finds a way to maintain its increased level of investment in the service, it warned.

The study looked at what would happen after 2008, when the current annual funding increases of 7% are due to end.

It calculated that the NHS will need 4.9% rises every year after that to sustain better services, but that the Treasury would probably only be able to afford 3.5%, leaving the health service £11bn short by 2015.