Now, chocoholics have a justified reason to savour their favourite sweet, for a new study has found that eating chocolate can help stop bowel cancer.

Scientists say that the key is a naturally-occurring chemical in chocolate. Tests on a man-made version of the chemical showed it halved the rate at which tumours grew, leaving healthy cells untouched.

The man-made creation is a copy of procyanidins, a class of molecules thought to protect the body's healthy cells.

Procyanidins are powerful antioxidants found in large quantities in cocoa beans, the main ingredient for chocolate.

For the study, scientists at Georgetown University in Washington DC used doses similar to the amounts that someone might eat if they snacked on chocolate occasionally.

The team says that their findings make the case for some of the properties of chocolate as a cancer treatment.

Researchers tested GECGC, a synthetic version of the chemical made by confectionery giant Mars, which partly funded the study. They exposed 16 different types of cancer cells to the chemical and found that it had an effect on four.

The results showed that the strongest response was seen in two types of bowel cancer cells, where tumour growth was slowed by 50 per cent - and malignant cells damaged by the chocolate chemical.

However, it remains unclear exactly how the chocolate chemical works on tumours.