>>4290465Real explanation - British teeth were, historically, very bad because dentistry, beyond emergency dentistry, was not covered by the National Health Service. In the first 30 years after the NHS, then, dentistry - outside of providing services to the ultra rich - was not a good profession, especially compared to Medicine, which in the UK share roughly the same entrance requirements. There was a dearth of dentists. On top of that, orthodontistry was considered a cosmetic surgery, so had extra tax attached to it. Furthermore, our prolific tea drinking lead to wide spread staining (which again was considered a cosmetic surgery to clean off) combined with our national love of sweets.
In the present day, with changes to the NHS which mean that dentistry is actually a very lucrative profession, most people have very good teeth, except of course the ultra bydlo, who's pictures are often shown here as an example of "general British teeth".
I would say that it does tend to be true that British people have crooked teeth in general and most people require braces. Why that is I do not know.