Access to NHS weight-loss surgery is "inconsistent and unethical" with some obese patients effectively being made to eat more to get an operation, doctors' leaders said today.

The Royal College of Surgeons (RSC) said NHS funding constraints meant some patients who already qualify for operations are being forced to wait until they are more obese or develop life-threatening illness like diabetes.

It has calculated that out of around 240,000 people requiring weight-loss surgery, only 4,300 - or 2 per cent - had operations carried out last year.

The college also said that approximately two thirds of surgeons saw patients eligible under national medical guidelines being refused surgery in their centres.

Under NHS rules, morbidly obese patients - those with a Body Mass Index (BMI) of 40 or more - have a right to be assessed for weight loss surgery.

The RCS said while some health trusts observe the guidelines, others stipulate that only the most extremely ill patients - those with a BMI of 50 or 60 with obesity related illness - are referred for surgery.

RCS education director, Professor Mike Larvin said: "National Institute for Health and Clinical Excellence (NICE) guidelines are meant to signal the end of postcode lotteries, yet local commissioning groups are choosing not to deliver on obesity surgery.

"In many regions the threshold criteria are being raised to save money in the short term, meaning patients are being denied life-saving and cost effective treatments and effectively encouraged to eat more in order to gain a more risky operation further down the line."

The RCS said the delay in treating obese patients was draining NHS resources, with obesity associated healthcare costing an estimated at £7.2 billion annually.

It is calling for the Department of Health to ensure that all patients have equal access to treatment.

Dr David Haslam, chairman of The National Obesity Forum, said: "(Weight-loss) surgery is amongst the most clinically-effective and cost-effective specialities in any field of medicine, preventing premature death, and transforming lives, whilst saving vast amounts of money for the NHS and the economy.

"Even the most cynical taxpayer should, alongside clinicians, in opposing the unethical and immoral barriers to surgery imposed by NHS purse-string holders."

A Department of Health spokesman said independent guidance on obesity from the NICE recommended that "drugs and surgery should always be a last resort".