Britain's growing obesity problem has prompted the use of ambulances capable of carrying people who weigh up to 285kg, or 45 stone.

The vehicles also have special stretchers to lift patients with less embarrassment.

One of the first has started work in South Yorkshire, after assessments of local obesity justified the £64,000 cost. The Mercedes ambulance already has 12 patients on its list for hospital journeys. There are estimated to be 1,500 potential users in the county with health problems who weigh more than 120kg.

Similar "bariatric" or seriously overweight cases previously had to travel in the back of a van otherwise used to carry heavy equipment to major incidents. Sometimes, including the transport of a Rotherham man in his 40s, fire brigade equipment has been used for safe lifting.

"It was undignified and caused embarrassment," said Peter Ward, director of operations for South Yorkshire ambulance service. "The general public are getting larger, and not all of it is because people are going to McDonald's."

Some of the most problematic cases, including the Rotherham man, are due to medical conditions that medical staff fear could be worsened by stress over humiliating transport.

Mr Ward added: "The new vehicle doesn't attract attention and the patients appreciate it."