A group of NHS hospitals stand accused of fiddling their waiting lists to meet ministers' targets, according to a report by the government spending watchdog.

The National Audit Office concluded in its report published on Wednesday that in nine hospitals the culture of list adjustment was "ingrained".

More than 6,000 patients are believed to have been caught out by the practice with hundreds forced to wait longer for their operation because of the practice.

The NAO also recommended the management at a further 13 hospitals should be investigated because of suspiciously high numbers of patients suspended from waiting lists.

Sir John Bourne, auditor general, believed the scandal had come about because the government had sent out a "very strong message" that waiting lists were a high priority.

"The adjustments were made in the context of pressure on trusts and particularly chief executives to meet key departmental targets," he said.

Nigel Crisp, the NHS chief executive, expressed his concern over the report's findings and anger at the hospitals involved.

"I expect, and the public have a right to expect, higher standards from NHS managers than this. Nine out of 300 NHS trusts distorted their figures and the numbers of patients involved are very small set against the five million who have an NHS operation each year. But the principles involved are important ones and I take this report very seriously," he said.

"This will be supported by a new code of conduct for NHS managers. Anyone breaching that code of conduct will not be re-employed as a manager any- where in the NHS."

Conservative shadow health secretary, Dr Liam Fox, blamed the government's targets for the scandal.

"This is a day of shame for Labour. The National Audit Office has confirmed what most people have believed for some time. The NAO report makes it clear that these fiddled figures are only the tip of the iceberg," he said.

"Labour's obsession with list targets, even at the expense of patients care, is resulting in systematic and widespread manipulation of figures in the most cynical way. This report finally blows ministers' cover by shining a light on one of the murkiest aspects of Labour's management of the NHS."

Evan Harris, the Liberal Democrat health spokesman, said: "If people with disciplinary records are being re-employed in this way, it says something about the skills required of an NHS manager. You have to ask why were managers doing this in the first place. I believe they did it because they thought they were doing the Government's bidding."