I can usually find cans of pumpkin in the American section at Tesco, but not always. Check the world foods aisle of your big shop and see if they have it in the American section. Otherwise, you'll probably need to order it from trusty old Amazon. You can usually get a few cans of pumpkin puree at a time, and then just keep them in the pantry until you're ready for your next pumpkin bake.