We were with John Lewis Pet Insurance for our cat. We did have to make a couple of minor claims for around £200-£300, which in fairness we easy to do. However, our premium soon shot up from around £13 p/m to around £40 p/m. We’re now with PetPlan but the only downside is that moving to a new insurer means that any pre-existing conditions are exempt.
In hindsight, I don’t think I’d bother claiming for small vet bills, as the premium increase probably worked out more than the vet bill.
Another consideration is whether you go for a policy with lifetime cover for a treatment or condition for a non-lifetime policy.