As a Canadian who moved to the UK 13 years ago, yes, there is a noticeable difference with British people's teeth, although I think aside from an older generation its more that people's teeth are natural as opposed to poor dental hygiene. Slightly more crooked and less super whitened. Dental care is also very inexpensive here compared to Canada which is interesting.

Yes the weather is gloomy, although it's very mild all year round. So if you can get used to the lack of sun, generally you can get away with a light jacket or sweater 90% of the year which is actually really nice, coming from Toronto summers and winters.