The Government’s attempt to extend water fluoridation across England is likely to focus on the most deprived 20 per cent of the population, which experiences 80 per cent of the nation’s dental disease.

Dentists say that in countries where water fluoridation is widespread, such as America, Australia and New Zealand, dental health is far superior to this country’s.

It is also better in those parts of the country where the water is treated compared with those where it is not. In a letter sent by Prof Raman Bedi, the chief dental officer for England, to health chiefs, he referred to the ”duty” of primary care trusts to reduce health inequalities. But these areas of need rarely coincide with the boundaries of water companies, and partial fluoridation can pose technical difficulties.

Prof Bedi’s letter sets out the legal procedures that need to be followed if the health chiefs are to instruct water companies to fluoridate their supplies. These include wide consultation with the local communities affected.

The Department of Health is drawing up a ”model agreement” covering the main terms to be included in any arrangements between England’s 28 strategic health authorities and the water companies. Under regulations introduced this year, health authorities are expected to carry out a public opinion survey, set up focus groups and consider all letters and resolutions.

They can go ahead with a scheme if they are ”satisfied that the health arguments in favour of proceeding with the proposal outweigh all arguments against proceeding”. Anti-fluoride campaigners say that the science is unproven and that fluoridation poses significant risks to health. Critics also claim that fluoridation is “indiscriminate mass medication”, and should not be forced on people against their will through their water supply.

Supporters say the biggest argument in favour of water fluoridation is that it works.

Although a large group of people mistakenly believes its supplies are fluoridated, only a small part of England is covered by schemes, principally around Birmingham and eastern England. The last major battle over fluoridation took place in the early 1990s in the North-East, where health authorities, backed by 70 per cent of the local population, had a scheme that would have covered one million people rejected by Northumbria Water, and then in the courts.

This year, Southampton City Primary Care Trust became one of the first to consider asking the health authority to use the new powers to introduce fluoridation.

Andrew Mortimore, the city’s director of public health, said: “Child dental health in Southampton is particularly poor. There is plenty of evidence that proves fluoridation can reduce decay.”