Health authorities are to prepare for the extension of mass fluoridation of drinking water to millions of people in a drive to improve dental health, following approval for the first new scheme in England for more than 25 years.

Opponents, who consider the scheme mass medication, yesterday failed to stop plans for the small scheme in Southampton and south-west Hampshire, paving the way for far bigger schemes across the rest of the country.

Authorities in north-west England, Derbyshire, Bristol, and Kirklees in West Yorkshire are thought to be among those preparing to press on with similar proposals.

The proposal, which affects around 200,000 people, had been seen by both sides as an important test case for the government’s drive to add the compound to water supplies as an important public health measure. The South Central Strategic Health Authority decided to go ahead with the scheme, put forward by Southampton city primary care trust, despite opponents outweighing supporters in a public consultation and a phone poll which it commissioned.

About 5.5m people, around a ninth of the population in England, already have fluoride added to their drinking water, while another 500,000 have fluoride naturally occurring in their water supplies. The Scottish government decided not to pursue fluoridation more than four years ago.

The government has been trying to extend fluoridation for years, having changed the law in 2003 to enable health chiefs to order, rather then request, water companies to add fluoride. It argues the practice cuts tooth decay and reduces inequalities with the benefit spreading to adults, adding that existing long-established schemes both in the US and other pasts of England, especially the West Midlands, have thrown up no evidence that it is harmful.

Opponents say there are potential health risks including bone cancer and hip fractures in older people, as well as lower IQ in children. The evidence for water treatment cutting tooth decay is not clearcut, they say.

Elizabeth McDonagh, chair of the National Pure Water Association, said it was considering possible legal action against the scheme in Southampton. She accused the health authorities of “blatantly promoting” fluoridation during the three-month consultation on the plan. Yet still 78% of more than 10,000 responses were against the proposal and a phone poll of 2000 people had shown more people were against the idea than for it.

“In the face of such opposition, the unanimous vote of the authority to fluoridate is a disgrace which shows from the beginning the consultation was a sham and a waste of public money,” she said.

Southampton City primary care trust (PCT) had argued fluoridation was the only way to reduce tooth decay in children across the city. Four in every 10 children have a filling by the time they start school in Southampton.

Health managers will now ask Southern Water to act, probably by 2010.

Bob Deans, chief executive for Southampton City PCT, said a water fluoridation scheme “when introduced with continued oral health promotion would be the most effective way of reducing the large numbers of tooth fillings and extractions currently needed by children in Southampton.”

Dr Andrew Mortimore, the trust’s public health director, added: “The safety and effectiveness of water fluoridation has been confirmed by a large number of respected health organisations, research from existing schemes which have been running for 60 years in the UK and worldwide, and the advice from internationally-respected local experts.”