This is a problem with Pakistani culture in Britain when it comes to marrying family members.
There's a reason why the hotspot of birth defects for all of Europe is in Bradford, an area of high Pakistani immigration where over 80% of married adult Pakistanis are married to cousins. That is an insane stat.
Brits have been doing this for literal hundreds to thousands of years.
No, some German-descended royals did it for a few hundred. And they are absolutely not representative of the average Briton. Most normal people aren't continually marrying from the same royal families of other allied nations, like royals used to.
Do you think maps like this are mere coincidence?