What kind of spider is this?
Thanks for the pictures! That's the European Garden Spider (Araneus diadematus)

They are most commonly seen from June to October, but they reach a peak around right now.  This species is all over UK, and is widespread in gardens, woodland, and meadows.  Here is another picture for reference:



Fun Fact: After laying their eggs in late autumn, the females die and only the eggs make it through winter.  Upon hatching, they look quite different from the adults: