Thousands of patients who want weight-loss surgery are facing a postcode lottery on the NHS, data suggests.

Some people who should meet the criteria for surgery are forced by their local hospitals to wait until they become even more obese.

Around one million people in the UK are thought meet the criteria for bariatric surgery, with around a quarter of these wishing to have it.

Guidelines from the National Institute for Health and Clinical Excellence (Nice) say people are eligible if they have a body mass index (BMI) of 40 or more, or a BMI between 35 and 40 with other significant disease such as diabetes or high blood pressure.

All other weight-loss methods - including traditional diets - must have failed for at least six months before surgery is considered.

An investigation by GP newspaper found more than half of NHS primary care organisations do not follow this guidance.

Data obtained under the Freedom of Information Act found 65 of 118 primary care organisations questioned rationed patient access to surgery, often by raising BMI thresholds to 50 or 60.

Some said they could not afford surgery for all those who wanted it.

NHS Stockton-on-Tees carried out the most procedures per population, with 5.9 operations per 10,000 people.

Meanwhile, NHS Rotherham funded just one operation among its 244,000 population, the investigation found.