I'm half British myself and I'd say the brits are a pretty ugly bunch and often have a weak bone structure. However, I think quite a lot of Northern Europeans are not especially attractive, not just British (after all we are a mix of celts, germans, french and dutch with a touch of viking) There is also the issue of plain colouring which makes people look uglier - here in the Middle East a lot of people look striking and attractive and in part it's features but also strong eyebrows, long eyelashes and dark hair and eyes play a part
I don't know what it is - genetics? My diet was good and I still have a small lower jaw. If you look at Iranians, a lot of them have really strong gonial angles...is it because there is some asian (mongol) blood from the Ghengis Khan? Living in a very mixed place, as well as British and some Northern Europeans, I also see a lot of Indians with poor bone structure, whereas some Pakistanis (especially northerners and pashtuns) have much more defined faces.
Brits do not have bad teeth, it's just that they 'got into' orthodontics later than Americans did
Don't forget that this is also an English language forum
Also I think Americans are more likely to get jaw surgery when they're teenagers. When I was a teen, jaw surgery in the UK on the NHS was very rare, but I was told that now it's more common. So there are quite a number of Brits with bite issues that had orthodontic work when they needed surgery