ManyPets - the £15k lifetime cover whch PP has (which actually is a lot of cover, because it's £15k per year with each issue covered for life).
So far I've claimed around £12k. They have paid out without issue, often paying me within 4-5 hours of the claim going in but for the larger claims, paying the vet direct.
Really would recommend them. The only other I would go with is PetPlan, but their top level was not as high as Many Pets for a few things, which is why I chose them in the end.