a big factor contributing to tooth decay is the flora of your mouth, which form different bioplaques, with different acidities, and different impacts on your enamel. The typical ecology of the british mouth may actually lead to more cavities.

other than that, the genetics of the population may impact the actual tooth structure, i wonder, as britain has seen a huge influx of new people over the last few decades, whether tooth problems have gone down on average?

This submission has been removed because it involves current events. To keep from discussion of politics, we have a 20-year rule here. You may want to try /r/ask_politics or another current-events focused sub.

It is true that by a small margin, the average Briton's teeth are less 'aesthetically appealing' than the richer areas of the US. However this does not necessarily mean that their teeth are any less healthy. In Britain less emphasis is put on the way teeth look to the extent where there is some resentment that they are mocked while many Hollywood stars have teeth which a lot of British people would find un-naturally white or perfect in term of structure.