A genetic abnormality that makes people hungry between meals is behind the problem of obesity among almost 50,000 Britons, say scientists at the University of Cambridge.

The gene mutation prevents approximately one in every 1,000 individuals from identifying the presence of the hormone that normally tells the brain when they have eaten enough.

Scientists say that up to one per cent of obese people find it virtually impossible to diet due to the abnormality in the hypothalamus, a part of the brain that plays a central role in hunger.

"The vast majority of these people have already been along the diet route. They have tried intense attempts to lose weight and it simply fails," the Telegraph quoted Steve O'Rahilly, Professor of Biochemistry and Medicine at the University of Cambridge, and one of the researchers who identified the abnormality, as saying.

"They are fat for a reason. They have impaired ability to remain satiated between meals because they have a molecule that is broken in their brain - it does not transmit the signal that tells them when they are full," he added.