Clinical priorities are being skewed to deliver a reduction in waiting lists, the National Audit Office (NAO) has claimed.

In a report published on Thursday, the NAO found that over 50 per cent of consultants had been forced to treat more routine patients over those suffering serious and potentially life-threatening illnesses in order to meet Department of Health targets.

One in five of the consultants interviewed said that clinical priorities were distorted on "a regular basis".

Complex operations were often delayed in order to rush through high numbers of routine patients approaching the 18-month waiting time commitment, consultants claim.

Of the 558 consultants questioned, 113 said they often treated patients approaching the 18-month target for in-patient surgery instead of those in urgent need of treatment.

The report points out: "There is a risk that with pressure to reduce waiting times further, the failure to treat patients in accordance with their clinical priority will continue to be a problem unless waiting lists are managed effectively."

Dr Liam Fox, the shadow health secretary, said the report backed up Tory claims on waiting lists.

"This report conclusively proves what the Conservatives have said for years; that the Waiting List Initiative distorts clinical priorities. All around the country doctors have been angered by the way clinical need has been overtaken by political expediency. Those patients who have suffered deserve nothing less than an apology from Tony Blair," he said.

The health secretary, Alan Milburn, said the report was correct in identifying waiting times as a key issue for patients.

"The NAO is absolutely right to highlight waiting times - waiting for treatment is distressing for patients and frustrating for NHS staff. We are building on what the NHS has achieved in cutting waiting lists to now focus on reducing waiting times for treatment," he said.

David Davis, the chairman of the influential Public Accounts Committee, said ministers must take on board the report's criticisms.

"There must be no backsliding from the fundamental principle that those in greatest need are treated first,'' he said.

The report also reveals significant disparities in waiting times across the country.