Britons who have a high risk of developing diabetes know very little about the illness and are vulnerable to serious complications, health experts said on Wednesday.

Less than a third of patients most likely to suffer from diabetes know that it can lead to heart disease and only a quarter are aware it is linked to stroke, according to a MORI survey.

“This low level of awareness is frightening. Diabetes is a serious condition and prevalence is increasing rapidly,” said Douglas Smallwood, chief executive of Diabetes UK.

Ignorance about Type 2 diabetes means that many people have the illness for up to 10 years before it is diagnosed. By the time it is picked up, half of patients show signs of complications such as heart disease, stroke, blindness, kidney damage and nerve disorders that can lead to foot ulceration and amputations.

Diabetes is a chronic illness caused by a deficiency or lack of insulin. The hormone produced by the pancreas helps glucose, or sugar, from food get into cells.

If a person does not produce enough insulin or if it isn’t used properly by the body, glucose stays in the blood. People with Type 1 diabetes fail to produce insulin. Type 2 diabetes, the most common type of the disease, is caused by an inability to make enough, or to properly use insulin.

About 1.8 million people in Britain suffer from diabetes and experts estimate there are one million more who do not know they have the disease. About 90 percent of sufferers have Type 2 diabetes, which is linked to being overweight or obese.

People who took part in the survey were classified as high risk if they had two or more risk factors, which include having a family history of the illness or a waist size of 35 inches (89 cm) for women and 40 inches (101 cm) for men.

Black and ethnic minorities aged 25 and over and whites 40 years and older who are overweight or have a family history of diabetes are also high-risk groups.

“If the government is to deliver on its public health promises, it has to commit itself and the National Health Service (NHS) to educating people,” said Smallwood.

“People need to know the risks and what they can do about them,” he added.