So on Wednesday night I contacted pets at home via their website about the issue with the cat food and how to get a refund. The following morning I went on live chat to see if I could get a quicker response.
Anyway I got an email back from them today basically saying that if I had ordered food from them in store or online, they will cover consultation fees at the vets and the costs of blood tests if the vets deem it necessary, as a sign of goodwill.
If you're worried about your cats after they've eaten the food, it's worth enquiring with pets at home about covering cost of vet fees. Obviously they'd need invoices from the vets and your cats medical history.
Hope all your cats are still healthy and doing well 👍