MPs will tonight debate a York University report on one of the most controversial issues in public health - putting fluoride in drinking water.

The Government commissioned the research into the implications of fluoridation from the university's NHS Centre for Reviews and Dissemination (CRD).

Now Sunderland North Labour MP Bill Etherington has secured a late-night debate on the report in the Commons, when Health Ministers are expected to attend and answer questions.

The CRD paper was published last October. Among its most important conclusions were that fluoride did appear to prevent tooth decay, and that there did not seem to be a link between fluoridation and serious conditions like cancer, bone fractures and Down's syndrome.

On the other hand the report also found that there was a higher degree of fluorosis - or mottled teeth - associated with the process than researchers had expected.

CRD director and co-author of the report Professor Jos Kleijnen said when it was published that this was an issue which had polarised public opinion for over 50 years, and given that background he and his colleagues were surprised by the "disappointing" quality of previous research work in this area.

Professor Kleijnen added he was pleased he did not have to make decisions about fluoridation, with a balance to be struck between reducing tooth decay by 15 per cent, and the fact that up to half of the population could be affected by fluorosis.

There were also ethical, legal and environmental concerns. "A lot of people think what comes out of the tap should be pure and clean and free of additives," said Professor Kleijnen. "I'm quite happy I don't have to make that decision." Two months after the report was published there was further controversy when Professor Trevor Sheldon, of York University's Department of Health Studies, claimed its results had been "widely misrepresented".

He stressed that the review's findings were more cautious and less conclusive than most previous ones, adding that it did not show fluoridation of water to be safe. "The report recommended that more research was needed," said Professor Sheldon.

Updated: 11:19 Monday, January 29, 2001