Some seriously ill patients are being forced to make way for less serious cases to help hospitals meet waiting list targets, a new report claims.

A leaked draft report by the National Audit Office (NAO) says consultants are changing their priorities under pressure to meet national waiting list targets.

It means patients who have been waiting a long time could be treated sooner than patients who might have worse conditions but have not been waiting as long.

National standards say patients must not wait more than 18 months to see a consultant.

The national report, called Waits and Measures, interviewed 50 hospital management trusts in England.

Sussex hospitals say they operate strict criteria on treatment of patients on waiting lists. But they admit that increasing national pressure to meet standards has raised concerns.

Brighton Health Care NHS Trust says while it ensures emergency cases are dealt with first, clinicians often have to juggle cases to meet targets.

Spokesman Ian Keeber said: "It is a difficult situation. Obviously it is unacceptable if a patient has to wait 18 months, but then we are left with a scenario where that person could be seen before a more serious case so we can meet the Government standard.

"However, we would never put a long-waiting patient before a potential emergency case. It is a question of the demands we have to meet and the limited capacity we have to meet them."

Worthing and Southlands NHS Trust, whose waiting list has fallen from 6,400 to 5,500 in the last year, says the way patients are treated depends on the scale of their illness.

Spokesman Pam Lelliott said: "The trust operates a policy of classing patients as very urgent, semi-urgent and routine when they are placed on the waiting list and they are treated accordingly."

A spokesman for Eastbourne Hospitals NHS Trust said: "We were not one of the trusts called to participate in this audit and the definitions we use to prioritise patients are in line with national and regional policy."

In the East Sussex, Brighton and Hove Health Authority area there are currently 18,136 patients on the waiting list compared with 18,664 last year. In West Sussex the figure is 18,837, compared with 19,446.

The draft NAO report says waiting times are a major public concern although most patients receive a good service from the NHS.

The average wait for admission to English hospitals is more than seven months but one in four people has to wait longer than 18 months.

The report estimates the real waiting time for patients, from seeing their GP to hospital admission, is on average 219 days. It says 25 per cent of patients may wait as long as 563 days.

The Department of Health said in a statement: "This is a draft NAO report which, like all other NAO reports, has been sent to the Department of Health to check for factual accuracy.

"The department is currently agreeing factual amendments with the NAO. In the meantime we will not be commenting directly on a leaked document."