A 'wonder' diet pill that promises to suppress appetite without causing nasty side effects, has been developed by scientists.

The new drug, OAP-189, switches off the appetite by mimicking the effect of a hormone that is released naturally in the stomach when it is full.

Increased levels of the hormone, oxyntomodulin, are also found in people who have had gastric bypass operations, in which the stomach is made smaller.

Professor Stephen Bloom, a world-leading expert in obesity at Imperial College London, who developed the pill, looked for a way to mirror the procedure’s weight loss benefits without the need for surgery.

He said: "I think we could mimic the dramatic weight loss achieved with stomach bypass surgery by giving people gut hormone-derived therapies. If you could take away hunger, food is not attractive."

The only existing prescription-strength diet pill on sale in the UK is Xenical, which has been sold under the name Alli since 2009. This prevents the absorption of fat but can cause nasty side effects such as diahrroea.

Early trial results of the new drug are looking hopeful. Overweight and obese volunteers lost an average of 5lbs in four weeks after being given three daily jabs of the hormone.

The drug has been bought by Pfizer, the pharmaceutical giant that brought us Viagra, and is now in the early stages of human trials. However, it could take between five and seven years before it is available on the UK market.

Initially it is likely to be prescription only and aimed at diabetics but in time could be sold over the counter in chemists, the Daily Mail reported.