Its a stereotype of the British, think of any cartoons you see of British people and they'll normally have buck or uneven teeth. We have NHS dentists but their main aim is to prevent decay and pain at a reasonable cost for all. It costs a fair bit of money to whiten and straighten your teeth, so many people don't have the option. Post WWI & WWII we lost a large amount of our nations men, this lead to a weaker and reduced gene pool and sadly bad teeth.