Good morning and welcome from the UK!
Not sure that this is really going to help you - but we had exactly the same problem with Harry when we first brought him home. He seemed to think that pee pads were his latest toy - not use them but either shake them around, or fetch them to us!
So instead we did the 'designated place in our back garden' thing - picking him up and taking him outside after every normal trigger point (at least once an hour during the day) until he went to the backdoor himself, asking to go out. This took about a fortnight in all of being very, very consistent and vigilant - but it did work, and it was so worth it!
Good luck! Sally + Harry x