Obese people should not be banned from undergoing knee and hip replacement surgery because there is no evidence they fare any worse than thin patients, doctors said today.

Their comments came after it emerged that some NHS trusts are only allowing people of an average weight to undergo these operations in an attempt to cut costs.

Under new rules introduced by three primary care trusts in east Suffolk obese people will not be eligible for hip and knee replacement surgery unless all other treatments have failed to alleviate their pain and disability. The trusts admitted that the eligibility criteria had been introduced in a bid to save money.

But Professor Paul Gregg, past president of the British Orthopaedic Association, said if rationing had to be carried out it should be done on the basis of clinical need, not on a person's weight.

He said: "I'm not opposed to rationing but the way to do that is not to get rid of the fatties. Those who most need surgery should get it. There are some people devastated by osteoarthritis but others for whom it's a nuisance while playing golf.

"If someone is very fat and their surgeon is prepared to operate, and they're prepared to accept the risks, why the hell shouldn't it go ahead? In the long-term the failure rate of hip and knee replacement surgery has never been shown to be worse in fat people than in thin people. Indeed, people sitting around getting fat are less likely to put their new joints under stress."

The othopaedic surgeon added that if the NHS needed to save money, minor operations, such as those to correct bunions, should be restricted rather than joint replacement.

The British Medical Association also criticised the eligibility criteria. Dr Jonathan Fielden, deputy chairman of the BMA's consultants' committee, said: "The decisions on whether patients should receive treatment should always be based on clinical need and not solely financial reasons."

The Patients Association also said the ban was unfair. A spokeswoman said: "People are obese for all sorts of reasons. Unless there is a clinical reason for not carrying out surgery they should be entitled to have an operation as anyone else would be."

Under the east Suffolk rules, hip and knee replacement surgery will only be offered to obese people if their pain and disability is "sufficiently significant to interfere with [their] daily life and/or ability to sleep".

The eligibility criteria are based upon a person's body mass index (BMI), which calculates a person's body fat percentage using a height-versus-weight calculation. A person of average weight has a BMI between 18.5 and 24.9, while a score of 30 or above rates as obese.

A spokeswoman for the Norfolk, Suffolk and Cambridgeshire strategic health authority said: "Patients will be assessed according to their clinical needs, as is the norm, and if necessary advised to lose weight before treatment, which will reduce the risks and improve outcomes for surgery.

"The message is that patients who need clinical treatment will get it."