I don't know why, but the practice I used to be with wouldn't claim direct from the insurance. They insisted customers paid themselves and then filed paperwork to reclaim from insurance. I guess that way they always have their money...

My current practice will allow you to just tell them to claim from your insurance. Then I get an email from Direct Line saying that they've been paid by our vet. It's especially great with ongoing claims - like for allergies. It basically makes the experience feel like the NHS for dogs, with no money changing hands when you go to the vet