'Keep it in the family, I say, ' quipped Alan Milburn as he fielded a question from Ann Winterton the other day. The Conservative MP for Congleton has been campaigning to save the heart transplant centre at Wythenshawe, Manchester, and doing it, she revealed, with the support of the MP for neighbouring Macclesfield, her husband Nick.

Actually, it wasn't the Wintertons' concern about their much-valued centre that caught my attention.

The word that stopped me in my tracks was 'fluoride', a controversy I do not recall hearing about since the days of Sir Ivan Lawrence, the Tory QC and libertarian. Fluoride was one of his obsessions and he once made a sevenhour filibustering speech in the Commons to prove it.

But here we were in 2001 with Mr Winterton asking a vintage Sir Ivan question about government plans to introduce legislation to enforce fluoridation of drinking water. Why? And why does Labour's David Hinchliffe, Mr Winterton's successor as chair of the Commons health select committee, agree with him?

When I rang both MPs, I found that they are both Lawrence-ites, concerned about the principle of what Mr Winterton calls 'compulsory mass medication' and about what Mr Hinchliffe calls the 'negative wider effects' of fluoride, which range from severely discoloured teeth to (hotly disputed) cancer, bone fracture and even Down's syndrome.

'A lot of people are vigorously opposed, not just cranks, ' insists the Wakefield MP.

Better off people can avoid the stuff by buying bottled water (the nonfluoridised kind, I assume), poorer voters have no choice, he says.

But why does it matter now? Because the restless Mr Milburn has asked the Medical Research Council to look for fresh evidence (either way) on the back of a report last October from York University.

The York report discounted ('no association has been shown') the worst fears about fluoride and concluded that health authorities with the worst dental problems have better teeth if they operate within a fluoridised water area. Ditto the bestperforming areas.

As it turned out, both MPs were reassured by the reply given to their interventions by junior health minister Gisela Stuart, more so than the Wintertons were by Mr Milburn's answer on the Wythenshawe heart centre.

Ms Stuart, on the other hand, combined enthusiasm for fluoride and extra cash for Cheshire's dentists with a warning that ministers are telling eager local authorities that 'the majority of the population would have to be in favour' before fluoridation could be allowed.

For Mr Hinchliffe, that sounds like a green light for local referendums, which he welcomes. It is consistent with New Labour's voter-sensitive approach on such touchy topics as grammar schools. It is not good enough to leave it to Yorkshire Water, acting with the agreement of local authorities (the current law), the MP says.

What surprised me in this controversy was to discover that, 40 years on, there are still only 5 million people in Britain (population 59 million) who have fluoride added to their water.

Most are in the West Midlands, with a further 1. 5 million getting it naturally, mainly in eastern England, from Essex up to Hartlepool, which probably explains why Peter Mandelson has such a lovely smile when he chooses.

Mr Winterton, a doughty right-wing champion of the NHS, admits that he got stuck into fluoride when he was a Warwickshire county councillor 30 years ago and sat through part of Sir Ivan's seven-hour odyssey.

'I am a regular teeth-cleaner and made sure my children cleaned theirs, ' says the former Hussars officer, who believes in choice. 'If people want fluoride, you can take it nowadays in tablets, toothpaste, even milk. '

So there.