Ian Gibson, a former chairman of the Commons Science and Technology Committee, made his remarks after it was disclosed that 345 children in Norfolk have type 1 diabetes — more than double the 160 cases that would be expected for the size of the population. In the past three years doctors have treated 42 new cases of the condition among children, compared with a national average of 24 for a county the same size.

“I would imagine it is linked to the fact that people in Norfolk are quite inbred, with many not leaving the county,” Dr Gibson, the Labour MP for Norwich North, told his local newspaper, the Norwich Evening News. “It is something that needs to be looked at as a priority, especially as many cases are linked to obesity too.”

When asked if he thought that people would be offended by his comments, he said: “Probably, but they are inbred. If you look at the names in Norfolk, there’s a lot that are the same. There is an inbreeding complex in villages — people intermarry. That might mean more of them have got the same gene, which predisposes them to it.”

Ketan Dhatariya, a consultant diabetologist at the Norfolk and Norwich University Hospital, described the MP’s remarks as disgraceful.

“It’s an insult to people with type 1 diabetes and their families and it’s an insult to people in Norfolk,” he said. “There’s no suggestion that that is the case. It’s not the way that the genetics work. There is a genetic element but it may be triggered by an environmental factor. Nobody knows why it is rising.”

Charles Joyce, a county councillor in Norfolk, said: “Dr Gibson has to be joking. I can’t imagine his comments going down very well around here. He can’t go around saying things like this without having the medical proof to support it. He needs to put up or shut up.”

Maria Lam, a spokeswoman for Diabetes UK, described the comments as “very insensitive”. She said: “Inbreeding is a very controversial word and has implications of incest . . . Clearly genes do play a factor because you are more likely to get dia- betes as a child if your parents have it.

“But we still don’t fully understand the relationship between genetics and diabetes and there is ongoing research into it.

“The fact that there has been a big increase in recent years suggests that genes actually might have less to do with it. We suspect that a mixture of genetics, environmental factors and infections all play a part.”

Ms Lam said that the number of type 1 diabetes cases among children aged under 15 in the UK had risen from 11,400 in 1996 to 20,000 in 2004.

Type 1 diabetes, also known as insulin-dependent diabetes, is commonly found in children, while the type 2 condition generally occurs in older people and is often caused by obesity.

Dr Gibson, 67, stood by his comments yesterday and insisted that he had not meant to cause offence. “If you have a high frequency of genes with a predisposition to type 1 diabetes, then you have to ask why that is,” he said.

“I am not talking about incest or anything like that. But it is the case that people in past generations did not move around so much and would have had relationships in their own communities.

“Inbreeding is one of those things that nobody can talk about because it brings up images of mutants — but that is not the case. Norfolk people are really no different to those in other areas of the country.

“My purpose in bringing this up is not to denigrate anyone but to try to understand why there is a high rate of diabetes among children in Norfolk.”

Times Recommends

• Madonna and her Guy decide it’s over
• Terror police target internet phone calls
• Red squirrels develop immunity to grey plague