A grandmother who weighs 17 and a half stone has been told she cannot have surgery because she is too overweight.

Evelyn Lang, 43, said consultants at the Royal Blackburn Hospital refused to operate on her ovaries, kidneys and bowels because of her size.

At 5ft 4in, her body mass index is 40.9. Health bosses say anyone with a BMI over 30 is obese.

The former care assistant, who has had to give up work because of her ill-health, said her weight was difficult to control because of the steroids she takes to control severe asthma.

Dr Colin Waine, chairman of the National Obesity Forum, said: "I understand the surgeons' concerns over increased risk, but there are obstacles to this lady losing weight, and instead of discharging her, the hospital should have referred her to a specialist weight-loss clinic so that she can have the surgery as soon as possible.

"For people who are ill, losing weight often is nowhere near as simple as eating less. Leaving the situation as it is and simply taking more painkillers is not the answer - people need a lot of support."

Mrs Lang, of Fishmoor Drive, Blackburn, has nodules on her kidney, cysts on her ovaries and needs an exploratory operation to get to the bottom of a bowel problem.

She accepts that none of the conditions are life-threatening but says she is in almost constant pain.

The operation to deal with her conditions was set to take place in July last year, but was cancelled on the day because Mrs Lang was found to be anaemic.

When she returned to the hospital in February, expecting to be given a second theatre date, she claims a surgeon told her: "You're too fat and I'm not going to operate."

When she went back again last week, she claims nurses told her she was being discharged as a hospital patient, and would have to continue managing her severe pain with high doses of morphine.

Mother-of-four and grandmother-of-five Mrs Lang said she was given no dietary or exercise advice from the hospital - a claim denied by bosses - and now feared becoming addicted to the strong painkillers.

Mrs Lang said: "There was nothing said about my weight when they were about to do the operation in the summer, so why have they started saying this now?

"I don't want to keep taking morphine - I have been on it a long time and they keep having to increase the dose because it's stopping working.

"I'm willing to lose weight and I've made an appointment with my GP to talk about it but I can't do a lot of exercise when I'm in so much pain, so I'm in a vicious circle."

She added that she was much heavier - weighing almost 20 stones - two years ago, when she was given surgery for a hernia.

A spokesman for the hospital said a range of health problems had meant it would be dangerous to operate on Mrs Lang, with her weight being a major factor, and that advice had been sent to her GP on health improvements needed before the operation.

The hospital's director of operations Val Bertenshaw said: "Under no circumstances would a medical professional advise that a patient be sent home and discharged without correct treatment or information from the professional concerned as to the reasons why a operation can not be carried out.

"Patient treatment and safety is our priority.

"The correct preparation for an operation is just as important as the operation, and to ensure that no complications arise during surgery the operating team and surgeon must ensure that a patient is strong and able enough to endure the strain and stress of an operation, so that the best outcome can occur."

The Lancashire Telegraph's medical expert Dr Tom Smith said Mrs Lang needed to lose at least three stones to decrease the risks.

He said: "Anaesthetics dissolve in the fat around the brain, and will dissolve in excess body fat in obese people, so it takes a lot more anaesthetic to put an obese person to sleep.

"Then there are more problems after the operation, because it takes them longer to wake up.

"The anaesthetic in the fatty deposits can later travel to the brain, meaning a real risk of the person never waking up.

"On top of that, the excess tummy fat rests on the chest when the person is lying down for an operation, restricting their breathing."

Mrs Lang said she was willing to take the risks and have the operation.

She said: "At the moment I have no life anyway. I even have to get someone to help me clean my house and I can't go out and do the things I want to do."