The finding raises the possibility of developing a vaccine for the disease.

The researchers have discovered a marked difference between the way the bodies of healthy individuals and those newly diagnosed with diabetes respond to a virus known as Coxsackie B4.

He said: "The implications are clear: if viruses have a proven role in the disease, there is the future possibility of developing vaccines to prevent infection and therefore Type 1 diabetes."

Type 1 diabetes is an autoimmune disease in which the body lacks insulin, the hormone which controls the sugar levels in the bloodstream.

People with the condition have to inject insulin daily instead.

Serious form

The disease usually begins in childhood, affecting as many as one in 200 people. It is also on the increase.

Both Type 1 and the more common Type 2 diabetes can lead to blindness, kidney failure and heart disease in later life.

The cause of the disease is not clear. However, it is most likely to be due to a complex interaction between a person's genes and their environment.

Various studies have suggested that a group of viruses could be a trigger, stimulating the immune system to attack and 'kill off' the cells that produce insulin.

But until this study the evidence has been indirect and the immune cells involved unclear.

Dying patient

The research team focused on the Coxsackie B4 virus (CVB4), a bug that causes typical viral symptoms and is most commonly found in children.

Several years ago, a strain of this bug was recovered from the pancreas of a child dying from Type 1 diabetes.

Using the genetic code of the virus and the latest DNA technology, the researchers were able to grow key parts of the virus.

They then tested how the body responded to the virus using blood samples from 40 Type 1 diabetics who had been diagnosed within the last five months.

The team found that CVB4 did stimulate the immune system very readily.

However, the response of the diabetics was more pronounced.

This suggests that the diabetics had been exposed to the virus in the recent past, or repeatedly over time, and so were already primed to take action.

The research, funded by the UK charity Action Research, is published in the journal Diabetes.