Lead researcher Professor Kay-Tee Khaw said: "The study shows that high sugar levels, even when they are below those of diagnosed diabetes, could be linked to increased risk of bowel cancer.

"More research is needed but if the results of our study are confirmed they would be important in developing prevention strategies." Professor Khaw believes that both diabetes and bowel cancer may share common predisposing factors. It is already accepted that a high fibre diet and regular exercise can help protect against both diseases.

Alternatively, hormonal changes associated with diabetes could promote tumour risk.

The researchers focused on a chemical called glycated hemoglobin. Not only does this give a good indication of blood glucose levels over the past few months, it also provides a clue about the metabolic processes in the body that influence levels of insulin - the hormone which breaks down sugar.

Around 35,600 people are diagnosed with bowel cancer each year in the UK. In men incidence rates have increased by an average of 1% each year over the last 20 years. Around two-thirds of cases may be preventable by changes in diet, including eating more fibre, and less fat.