Geology of Great Britain
The key thing to remember is that these rocks are very ancient, quite unlike relatively modern islands like Japan, Honolulu or the Galapagos. These are relatively new islands which are volcanic in origin. Quite different are the British Isles, which are formed from extremely ancient rocks which were part of ancient continents. That is why you can find almost any rocks known on Earth somewhere in the British Isles, but volcanic islands are limited in their rocks.