Although incredibly controversial, inbreeding in Britain is probably more common than you think.

One academic study examining rates of ‘extreme’ inbreeding – where parents of a child are considered to be first- or second-degree relatives – found 125 Brits out of a sample of 450,000 were the result of such unions.

First degree relations include those between parent and child, while second-degree includes more distant, but still genetic close relatives, such as half-siblings. 

Extrapolated to the wider population, the 2019 study was reported as meaning some 13,000 Brits were conceived through extreme inbreeding. 

The authors noted , given the nature of the subject and the limited variety of Brits included in the sample, true rates could be significantly higher or lower. 

This map, by Professor Alan Bittles an Australian expert in genomics, shows rates of consanguineous marriage, that between cousins, around the world

An NHS website hosting the Born in Bradford (BiB) research project describes marrying your cousin is a cultural practice similar to White British women and couples choosing to have kids after the age of 34, another risk factor for genetic conditions 

Of the 125 total, about 43 per cent were attributed to be the result of the first-degree relations, those between parents and children. 

Some were adopted as children and thus likely had no idea of their parentage. 

Incest — sexual intercourse between immediate relatives — is illegal in the UK even if consensual.

Marriages between certain blood relatives — as well as some step relationships — is also illegal.

However, it is legal to marry your cousin in the UK.

Cousin marriage – which falls under the consanguine bracket – was once common among Britain’s upper classes, with it historically seen as a way of firming up alliances and keeping wealth and land in the family.

While falling out of fashion, alongside other arranged marriages, the practice is still common in some UK communities.

Experts have previously written about how a preference for cousin-marriage among British Pakistanis was a contributing factor in child mortality rates in Bradford due to an increased risk of genetic conditions. 

NHS studies between 2007-11 found consanguineous marriage accounted for 60 per cent of marital unions in people of Pakistani heritage in Bradford.

This compared to just 1 per cent among white British couples in the area.

Of the Pakistani-heritage marriages, 37 per cent were to a first-cousin. 

Subsequent NHS studies, conducted between 2016 and 2020, have found the rate among that particular community has fallen to around 43 per cent.

The NHS has previously stated cousin-marriage cousin accounts for about a third of birth defects in leaflets distributed to families in Bradford.

Under a scheme tracking rates across the area, health chiefs describe cousin marriage as a cultural practice.

Wording still available online today states it is no different than white British people choosing to have children over the age of 34, in terms of increasing the risk of genetic conditions in a baby.

Worldwide, one in 10 people are thought to be a result of a consanguineous union. 

Estimates on consanguineous marriage prevalence around the world vary.

Studies have put Pakistan as having one of the highest rates globally at 65 per cent of unions. 

This graphic, from NHS material disturbed to couples in Bradford, explains some of genetic risks of having children with a close relative. Two parents with a recessive gene have an increased change of having a child with an inherited condition

This is followed by India (55 per cent), Saudi Arabia (50 per cent), Afghanistan (40 per cent), Iran (30 per cent) and Egypt and Turkey (20 per cent each). 

Other data sets used by genetic experts studying consanguineous marriage have put the UK as having a rate of 1 to 4 per cent, while the US has a lower rate of less than 1 per cent. 

Data suggests the risk of a child resulting from a union of first cousins developing a genetic condition is between 3 to 6 per cent.

This still means the majority of children born in such circumstances will be healthy, however, the increased risk is undeniable. It’s roughly double the risk compared to children from unrelated parents.

Potential conditions include birth defects, developmental delays, and genetic disorders such as blindness, hearing loss, neonatal diabetes, and limb malformations.

Risks broadly increases the closer the genetic relationship between the parents, as well as if there is a family history of such unions, as genetic errors can compound between generations.

During conception, children receive one copy of genes from each parent, with the harmful genetic mutations, known as recessive genes, typically overridden by healthier dominant genes.

But when closely related individuals have a child there is a decrease in genetic variations.

Scientific titans Charles Darwin (left) and the famous physicist Albert Einstein (right) both married their first cousins

Queen Victoria and Prince Albert were first cousins, sharing a set of grandparents

Former Iraqi dictator Saddam Hussein’s (left) first wife was his cousin Sajida Talfah. Musician Jerry Lee Lewis (right), of ‘Great Balls of Fire’ fame also controversially married his cousin Myra Gale Lewis Williams when she was just 13, he was 22 at the time

This may lead to recessive genes  not being overwritten and becoming dominant in a child, causing many types of congenital disabilities.

These can include low IQ, cleft palate, heart conditions, cystic fibrosis, and an increased risk of infant death.

An increased interest and availability of DIY genealogy kits, enabling people to track their genetic family history, is leading to many people uncovering uncomfortable truths about themselves and their relations.

This has, in part, lead to some people, including in the US, discovering they are the result of an incestuous union, or in some shocking cases learning they have married or had sex with someone who then turned out to be a close relative. 

First cousin marriages were once far more common and include some famous historical figures.

The father-of-evolution Charles Darwin married his first cousin Emma Wedgwood, and the famous physicist Albert Einstein married his first cousin Elsa Lowenthal.

Authors Edgar Allan Poe and H.G. Wells were also known to have married their cousins. 

The British Royal family have also, like many European nobility, engaged in consanguineous unions.

Queen Victoria and Prince Albert were first cousins, sharing a set of grandparents.  

In more modern times, former Iraqi dictator Saddam Hussein’s first wife was his cousin Sajida Talfah.

Musician Jerry Lee Lewis, of ‘Great Balls of Fire’ fame controversially married his cousin Myra Gale Lewis Williams when she was just 13, he was 22 at the time.