ALAN JOHNSON, the health secretary, will this week tell health chiefs in areas of England with the highest rates of tooth decay to add fluoride to the water supply to improve the dental health of poor children.

Johnson will argue that adding the mineral to tap water is necessary to prevent tooth decay among children who do not brush their teeth regularly.

The health secretary believes the measure is needed to cut health inequalities between children in affluent families whose tooth brushing is supervised and in households where children may not even own a toothbrush.

"I want the NHS to do much more to prevent rather than just treat disease," Johnson said.

"Fluoridation is an effective and relatively easy way to help address health inequalities - giving children from poorer backgrounds a dental health boost that can last a lifetime, reducing tooth decay and thereby cutting down on the amount of dental work they need in the future.

"We have a duty to help the areas with the worst records on tooth decay to discuss this issue and take the necessary steps to improve their dental health."

However, the blanket fluoridation programme will be opposed by campaigners who say the entire population will be forced to take "medication" because a minority fail to brush their teeth.

The National Pure Water Association said: "By presenting fluoridation as a means of preventing tooth decay, Alan Johnson confirms the practice is medication. Fluoridation is carried out by water companies in violation of their customers' human right to refuse consent to any medical intervention.

"Fluoride is only being added to prevent tooth decay among a relatively small proportion of the population, mostly children in deprived areas who do not brush their teeth. These children are already being identified and treated in more effective ways."

Some doctors argue that while adding fluoride to water supplies would cut levels of tooth decay among poor children, the long-term medical consequences are unknown.

Johnson points out that in the Irish Republic, where more than 70% of water is fluoridated, the average number of decayed, missing and filled teeth per child is just 1.3 compared with 2.3 in Northern Ireland, where fluoridation has not been implemented.

Fluoride is already added to water supplies in areas of northeast England and the West Midlands. Fluoride also occurs naturally in the water supply in some areas.

In America, 70% of people use fluoridated water and it has been added to the supply of all US cities. In Australia the figure is 67 per cent.

Of Britain's 10 primary care trusts with the best child dental health, seven have some fluoride, natural or added, in the water supply. In all 10 of the primary care trusts at the bottom of the tooth decay league table, tap water is not fluoridated.

Primary care trusts in Notting-ham, Manchester, Westminster and Bradford, which have some of the highest rates of cavities in children's teeth, are likely to be earmarked for fluoridation.

Water fluoridation is known to cause a condition called fluorosis, discolouring teeth. There are also medical fears that consuming fluoride for years may increase the incidence of bone fractures and cancers.

A study from Taiwan found a high incidence of bladder cancer in women in areas with a high natural fluoride content in water.

Last year three academics accused the government of using inadequate evidence to promote the use of fluoride. They said there was not enough evidence to conclude that the benefits of water fluoridation outweighed the risks.

The government is also considering adding folic acid to bread to help to prevent babies being born with birth defects.

Health on tap

- About 5m people in parts of the West Midlands, Yorkshire and Tyneside receive water with added fluoride

- Britain's first fluoridation scheme was introduced in Birmingham and Solihull in the mid1960s

- In America about 70% of people have fluoridated water and the compound has been added to the supply of all big cities. In Australia the figure is just less than 70%

- Fluorides are naturally occurring minerals that can strengthen the tooth enamel, making it more resistant to decay. They also reduce the amount of acid produced by bacteria on the teeth