The extraordinary recovery of Stephen Knox, 31, the first time an adult in Britain has been treated this way, is certain to lead to calls for more publicly funded cord blood banks to be set up. At present there are only two.

The usual last-ditch treatment for leukaemia sufferers is a transplant of bone marrow, which makes blood cells. This involves destroying the patient's existing bone marrow and replacing it with marrow from a family member or compatible donor. Hundreds of patients still die because they cannot find a match.

It has been known for some time that blood from newborn babies' umbilical cords, normally discarded at birth, contains stem cells which could be an alternative to bone marrow.

A handful of British children have been treated in this way but it had been thought that adults could not. Even if matching cells could be found from one cord, they would not be enough to repopulate the entire marrow.

Then Stephen Proctor, a consultant and leukaemia researcher at Newcastle University, heard by chance of operations in Canada where doctors had mixed matching and non-matching batches of cord cells together with remarkable success. On February 22, at Newcastle's Royal Victoria Infirmary, Professor Proctor's team injected a mixture of stem cells from the umbilical cords of seven babies into Mr Knox, from Middleton-St-George, near Darlington, Co Durham.

Mr Knox had been given a few months to live after chemotherapy had failed.

One of the cords was a perfect match: the other six were not. But instead of the body rejecting the unmatched cells, they appeared to act as boosters for the tiny number of matched ones, and Mr Knox began to recover.

The amount of blood which can be taken from an umbilical cord is about enough to fill a wine glass. But of that, only a tiny fraction - a few hundred out of billions of cells - will be the kind of stem cells needed to replace some six pounds of destroyed bone marrow.

To the astonishment of Prof Proctor, Mr Knox's white blood cell level was up to adequate levels by five weeks.

"I wouldn't have believed that was possible," Prof Proctor said. "Stephen is progressing much better than we thought he would and the transplant has worked much better and more quickly than we expected. It's a really exciting development and opens up huge possibilities. It has been carried out 23 times in the UK on children but never with an adult."

The two publicly funded cord blood banks in Britain - one in Newcastle, the other in London - have too little money to collect and store the amount of blood that would be needed for a comprehensive nationwide transplant programme.