Removing the yellow peril

More than 100,000 people in Britain last year paid to have their teeth whitened.

Techniques range from whitening toothpastes costing a couple of pounds to sophisticated cosmetic procedures favoured by Hollywood stars - and now Gordon Brown - which cost several hundred.

Power whitening - as used by the Chancellor - involves painting the teeth with a hydrogen peroxide gel and then a strong light which accelerates the bleaching action. It takes less than an hour and can lighten teeth by up to 10 shades by bleaching stain particles from food and drink which get trapped in the surface layersof tooth enamel.

Dr Phil Stemmer, of the Teeth for Life Centre in central London, said: "It is perfectly safe. The method does not remove enamel, damage teeth or increase susceptibility to gum disease."

But some researchers say that the chemical can weaken teeth and could even be linked to cancer. Other experts say power whitening is a "gimmick" which does not offer a long-term solution for stained teeth. Dr Martin Kelleher of King's College London said: "It will only last for a few months and then you will have to have it done again."

Whitening toothpastes also use hydrogen peroxide to bleach teeth, although in much smaller quantities. Many dentists say these have little or no effect on the colour of teeth. The other, somewhat cheaper, option for the Chancellor would have been a home bleaching kit costing around £100 from dentists.

This involves have a mouthguard custom-made to fit your teeth. Hydrogen peroxide gel is applied to the mouthguard, which is worn each night for a few weeks. Dr Kelleher said: "This technique takes longer to show an improvement but lasts around 18 months."