By Jane Elliott
BBC News health reporter
Pressure for surgery to treat obesity is so high that in some areas NHS lists are being closed to all but the most serious cases, the BBC has learnt.
1.2 million people in the UK are considered morbidly obese
In these areas, only people significantly above the minimum obesity measure are considered for operations.
Experts are warning there are simply too few surgeons trained in the field to meet rising demand.
The Department of Health said staffing had been increased, but local health bodies decided on patient priorities.
Weight is defined using the body mass index (BMI) measure, calculated by dividing weight in kilograms by the square of height in metres.
A BMI of 18.5 to 25 is classed as an ideal weight.
The National Institute for Health and Clinical Excellence (NICE) says patients with a BMI of 40, or 35 with an additional condition, are eligible for gastric banding or gastric bypass operations to reduce the size of the stomach.
But a patient group has said some areas have had to close their lists to patients with a BMI of less than 60.
Dr Roger Ackroyd, a consultant general surgeon and bariatric (obesity) specialist at both the Royal Hallamshire hospital and at the BMI Healthcare Thornbury hospital in Sheffield, said that his area has had to restrict its NHS list to patients with a BMI of 50, or 45 with additional problems, because there was no more capacity.
He said that, while the UK has 70 specially trained doctors in the field, only about half of them regularly carry out surgery.
"There are about 1.2 m people who fit the NICE criteria for obesity surgery in the UK, and there is no way that the NHS can cope with that with just 20-30 surgeons to carry out the work.
"I carried out about 400 of these operations last year and I will do the same number this year, or more. But I am just scratching the surface."
Dr Ackroyd added: "I don't think there is any easy answer. One of the answers would be to get people to eat better and exercise more, but the chances of this are unlikely."
His local primary care trust consortium, South Yorkshire/North Derbyshire and Bassetlaw PCTs, agreed the criteria had to be changed and said the situation was being kept under review.
Dr Ackroyd says about 30 doctors regularly carry out obesity surgery
Janet Edmond, director of British Obesity Surgery Patient Association (BOSPA), said that since surgery had been recognised as a viable option, this had led to increased pressure.
"We have heard of one PCT which says it will not accept patients with a BMI of less than 60."
But Dr Ian Campbell, medical director of the charity Weight Concern, blamed the NHS.
"The NHS is failing people because our job is to provide care and the supply of care is woeful.
"There are tens of thousands of people who would benefit from this sort of surgery, but are not getting it either because they are not aware of it, their surgeons are not aware of it or they do not meet the criteria."
A spokeswoman for the Department of Health stressed it was aware of the problems.
But she added: "Tackling obesity is not just about helping those who are already overweight, it is about preventing obesity in the first place and halting the year-on-year rise to protect our future.
"We have made significant progress in developing and increasing the size of the surgical services workforce but it is up to primary care trusts to decide what the local priorities are for their community and what services they should offer."