The author of the Discworld series describes the fillings - which millions of Britons have - as "toxic waste".

"Having something like mercury in your mouth seemed to me to be a really bad idea and I got rid of the stuff," said Pratchett.

Dental amalgam fillings, which contain 50% mercury, are under renewed scrutiny, although there is no hard evidence to support his beliefs. More than three million were inserted last year in the UK. Sweden last month banned all mercury products, including fillings, and Norway and Denmark have done the same.

Campaigners including Dr Jenny Goodman, a London doctor who practises nutritional and environmental medicine, have linked the fillings to MS, chronic fatigue syndrome and gut problems. But the Department of Health said fillings containing mercury are not harmful, except for the small number of people who are allergic. However, it still recommends pregnant women to avoid having any inserted or removed.

Peter Ward of the British Dental Association said the safety of mercury fillings had been subjected to numerous reviews and none had found evidence that they increase the risk of developing serious illnesses.