Fluoride in drinking water is either a golden bullet that will produce better teeth or a poison that will be forced on people every time they run a tap.

Dentists want the fluoride added, saying at low levels it has no effect on health and would help thousands of children grow up with healthy teeth.

The Government backs that view and, in an amendment to the Water Bill, wants to give health bosses carte blanche to order water companies to put fluoride in their supplies.

Opponents claim the substance is a poisonous by-product of the fertiliser industry and mass fluoridation would represent forced medication.

The latter belief was supported by Brighton and Hove City Council when, prompted by the Green Party, councillors voted by a substantial margin to oppose the move.

Keith Taylor, convenor of the council's Green Party group, said fluoridation would breach the European Convention on Human Rights and EU rules on medical intervention.

He said: "Fluoride is more toxic than lead, and only slightly less so than arsenic, and it should not be forced on people.

"If people want to have fluoride, they can buy fluoridated toothpaste but it should not be in the water supply."

The amended Water Bill, which could be law by the end of the year, closes two big loopholes.

First, strategic health authorities would be able to compel, rather than request, water companies to add fluoride.

Second, it would protect the water companies from prosecution, something the industry has always insisted on before backing fluoridation.

The existing loopholes mean only about four per cent of the British population so far has fluoride added to its water supply, mostly in the Midlands and North-East.

The National Pure Water Association has been campaigning against any increase to that percentage for more than 40 years.

Campaign director Jane Jones said: "Dentists have been taught at dental school fluoride is the best thing since sliced bread for kids' teeth. We are going to poison them because of a myth that it works and it is safe.

"How can you give people poison, toxic industrial waste and say this stuff is wonderful for reducing tooth decay?"

She said fluoride was not effective in preventing many of the most common forms of childhood tooth decay.

Ireland, where 72 per cent of the population drinks fluoridated water, came below the United Kingdom in EU league tables for dental health.

The city of Basle, in Switzerland, stopped adding fluoride to its water this year because it had not worked and the build-up of fluoride was proving bad for the environment.

Fluoride is an accumulative poison, according to critics, which renders sperm non-functional, causes infertility in women, depresses thyroid activity and causes crippling bone diseases.

The British Dental Association (BDA) claims opponents based their argument on exposure to high levels of fluoride and there was no evidence to suggest any of the side effects would be caused by adding the substance at the levels proposed.

Both sides agree fluorosis, a mottling of the teeth caused by continuous exposure, which requires special cleaning every four or five years, is an issue.

The BDA said fluorosis was a small problem. Critics described the condition as the first visible sign of fluoride poisoning.

Professor Liz Kay, who chairs the BDA's health and science committee, said fluoridation would reduce tooth decay and, in deprived areas, give children a better start in life.

She said: "The amendment to the Water Bill will give local communities the opportunity to decide whether they want fluoride added to their water supplies."

Southern Water said at the moment fluoride was not added to Sussex's water supply.

The company said it could not take a medical or ethical view on fluoridation and would want a clear message the public was in favour before agreeing to add the substance.

Among MPs who have signed a motion supporting fluoridation is Kemp Town's Des Turner, who said the evidence suggested there was less tooth decay in areas where fluoride occurred naturally.

He said: "I am generally in favour of anything which improves health and there is strong evidence modest, and I mean modest, levels of fluoride are good for dental health.

"I can see the civil liberties argument but you have to balance that against the arguments in favour of improving general dental health."