Alli capsules are slimming pills said to help people lose 50% more weight than they would through dieting alone. The pills went on sale over the counter yesterday in US but they may be available in Britain as well by the end of next year.

The Alli pills are the first of their kind to be sold without prescription. They represent a low-strength version of the prescription diet pill Xenical and cost about £1.40 a day.

Human trials showed that if one pill was taken with every meal, it would result in a 12-stone woman shedding more than half a stone, or one dress size, after just four months of regularly taking the pills.

However, the Alli capsules are not the miracle pills everybody has been waiting for years. It works only in with reduced-calorie, low-fat diets and exercise and offers its users a safe way to lose weight gradually.

Manufacturers GlaxoSmithKline intend to apply for a UK license later this year which means the pills may be available in Britain by the end of 2008.