The problem is worst among children born in Britain’s Pakistani community, where more than half of marriages are between first cousins, and children are 10 times more likely than the general population to suffer genetic disorders.

The medical risks of first cousin marriages include higher rates of infant mortality, birth defects, learning difficulties, blindness, hearing problems and metabolic disorders.

As adults, the children born from first cousin marriages are at increased risk of miscarriage or infertility. A third of children affected die before their fifth birthday. 

An investigation by Channel 4‘s Dispatches programme found that although more than 70 British studies have proved the risks, and 700 British Pakistani children are born with associated genetic diseases every year, many people deny the dangers.

Ann Cryer, the former Labour MP for Keighley, suffered abuse for trying to highlight the problems.

“It’s a public health issue and we deal with public health issues by raising awareness, by talking about subjects such as obesity, such as drug addiction, such as alcohol,” she said.

“But for some reason we’re told that we mustn’t talk about cousin marriages because this is a sensitive issue.

“I think it’s absurd, we have to talk about it in order to find solutions.”

Research shows the number of cousin marriages has risen dramatically in the UK over the last three decades, mainly between British Pakistanis, but also between first cousins in the British Bangladeshi community in which nearly a quarter of people marry their first cousins, and in some Middle Eastern and East African communities.