Like millions of other people in this country, he takes the appropriate treatment and leads a perfectly normal life

Cabinet Office spokesman

But he was able to live "a perfectly normal life", thanks to medication for the disease, the spokesman said.

Mr Prescott has been found to suffer from the milder non-insulin dependent, or "type-2" diabetes.

The spokesman said: "Like millions of other people in this country, he takes the appropriate treatment and leads a perfectly normal life, thanks to our excellent NHS and despite the press."

Diet changes

According to The Mail on Sunday, Mr Prescott, who celebrates his 64th birthday at the end of this month, had hospital tests because he was struggling to stay awake at work.

The paper said he was told by doctors to make drastic changes to his lifestyle and he was put on a strict diet.

The revelation about Mr Prescott's health is bound to reignite speculation - which he quashed earlier this year - that he may retire from politics.

In March, Mr Prescott denounced as "absolute trash" rumours that he was planning to step down.

But he admitted then that he no longer wanted the top job in the Labour Party.

Mr Prescott ran for leader in 1994 after the death of John Smith.

Inactive lifestyles

There are two main types of diabetes, which is a hormone disorder that can cause problems with the kidneys, legs and feet, eyes, heart, nerves and blood flow.

Type-2 diabetes develops when the body can produce some insulin, though not enough for its needs, or when the insulin that the body produces does not work properly.

It usually appears in people over the age of 45 who are overweight.

It can sometimes be treated by diet changes alone, or in combination with tablets or injections.

A spokesman for Diabetes UK said it would welcome any input Mr Prescott could make to its campaign.

"It's often something which people do not seem particularly willing to talk about. Given the numbers of people affected, we would have thought there would be more high-profile cases.

"We would certainly like to think Mr Prescott might be willing to help."