Critics say they need more proof that a bug found in milk could be the cause of a devastating bowel condition.

A London-based scientist, Professor John Hermon-Taylor, says he is convinced that that Mycobacterium paratuberculosis (MAP) is the cause of many cases of Crohn's Disease.

And traditional methods of making milk safe, such as pasteurisation, may not be able to protect the public, he adds.

However, other Crohn's experts say he has yet to prove a strong link between the bacteria and the disease, which can cause chronic diarrhoea, abdominal pain and weight loss.

Professor Hermon-Taylor said that his own work at St George's Hospital in London has found that MAP is present in the guts of people with Crohn's - and that the bug is well--known as a cause of intestinal illness in animals.

Residual levels of MAP exist in retail pasteurised milk in the UK, although there is controversy over whether these levels mean the organism could do any harm.

MAP is hardy enough to survive the 15 seconds of pasteurisation at 72 degrees which is enough to kill most other bacteria.

Another study suggested that MAP could be found in the breast milk of women with Crohn's, but not in the milk of women who did not have the disease.

A spokesman for the National Association for Colitis and Crohn's Disease said it was prepared to review any new evidence produced by Professor Hermon-Taylor.

But he said that the organisation was waiting for the results of two controlled studies before making any firm judgement.

The first of these, by the Ministry of Agriculture Fisheries and Food (MAFF) is looking at the occurrence of MAP in samples of pasteurised milk.

Another trial, in Australia, is attempting to treat Crohn's disease with a combination of antibiotics.

Professor Hermon-Taylor said: "The problems currently caused by MAP in the milk supply constitute a public health disaster of tragic proportions for which a range of remedial measures are urgently needed.

"I am absolutely certain that MAP causes a substantial proportion of Crohn's disease."

He is calling for a ban on unpasteurised milk, as well as an increase in the stringency of milk pasteurisation, and the widespread testing of dairy herds for the bug.

He also wants water supplies checked for MAP, and Crohn's made a "notifiable disease", meaning doctors must inform the authorities of every new case.

The research has been funded by Action Research.

Its director general, Anne Luther, said: "The extent of this problem appears far greater than CJD and Aids in the UK, yet previous calls for government action appear to have gone unheeded."