Doctors and surgeons at an Oxford hospital are taking part in a study to pinpoint why kidney transplants fail, forcing patients back on to time-consuming dialysis treatment.

The Churchill Hospital renal unit is one of five centres across the UK investigating the long-term prospects of patients who receive a new organ.

Staff hope their study, called Stepp (Study in Transplant Empowering Patient and Practitioners), will help improve quality of life, as well as reduce costs in the NHS, which spends an estimated £750m a year on kidney failure treatment.

About 3,000 people, including between 80 and 100 at the Churchill Hospital, are given new kidneys every year, from a deceased person or living donor who can survive with just one of two healthy kidneys.

But half the transplants fail within 10 years of the operation -- forcing the recipients to revert to dialysis, which replaces the kidney's role of filtering impurities from the blood.

Patients have to use the machine three times a week for five hours, which can restrict their normal lives.

If they decide to have another transplant, they join a list of 5,000 people and can wait more than two years for a suitable donor.

Each person on dialysis costs an average of £30,000 a year, compared to a one-off cost of £20,000 for a transplant and £6,500 a year for anti-rejection drugs.

Prof Kathryn Wood, professor of immunology at Oxford University's Nuffield Department of Surgery and a Stepp trustee who works with clinicians at the Churchill, said: "A transplant vastly improves patients' quality of life from when they are on dialysis, hooked up three times a week. It makes a huge difference to their ability to carry on a normal life.

"All organs are very precious and we want to make them survive for as long as possible.

"Obviously when you transplant a kidney you hope it will last a long time, but in some transplant recipients it fails and we understand very little about the reasons for that.

"It relies on a number of factors, such as the initial reason a patient needed the transplant in the first place and the anti-rejection drugs they are using.

Leicester Royal Infirmary, Guy's Hospital, London, St Helier Hospital in Carshalton, and St James in Leeds are also involved in the £280,000 Stepp programme.

Although it is only funded for three years, the researchers hope to monitor kidney transplant patients for five, 10 and 15 years.

Prof Wood said: "All patients are monitored very carefully, but there's never been a very systematic approach across the UK to really understand the common factors for long-term survival."