Continental UK said that I should get a new tyre fitted and they will look over the old one. They will then measure the remaining tread depth and refund the percentage difference i.e. 70% used = 30% discount off new tyre. They didn't sound concerned on the phone (maybe they have had to sort out quite a few people already?) a bit worrying really if it has happened that much
I'm getting the new tyre fitted on Friday so hopefully I'll get a result sometime next week.