The first significant attempt for more than 20 years to extend water fluoridation across England has been launched by the Government.

Health chiefs have been told to use new powers granted by Parliament to add fluoride to their supplies as a way of improving the oral health of their populations and to ''reduce inequalities''.

Under the 2003 Water Act, the 28 strategic health authorities now have the final say over whether fluoride should be added to the supply. That overturned a 1985 ruling that effectively left the decision up to the water companies, which were reluctant to fluoridate for fear of being sued and did not want responsibility for public health decisions.

Since then, no new scheme has been approved. However, water companies are now under a duty to fluoridate the water if they are requested to do so by a strategic health authority.

Fluoride is present naturally in virtually all water supplies but most levels fall short of the optimum for dental health, which is one part per million. For years ministers have wanted to see fluoridation expanded beyond the six million people currently covered by natural and artificial schemes.

A letter sent to health executives by Prof Raman Bedi, the chief dental officer for England, says the new laws provide a ''realistic option'' of doing so.

Such a move is enormously controversial and will provoke an outcry from anti-fluoride campaigners.

The Government says that there will be thorough local consultation before any new schemes go ahead and these will need to demonstrate "strong local support".

Opponents say the risks from fluoride are unknown, the science questionable and that studies have been equivocal in their conclusions.