Hi there - we are in Exeter. Issey was dx a couple of months ago and has been quite high - until we changed her food, now her numbers before jabbing are about 10 lower than they were and are normal if I test 4-6 hours after insulin.
Yes, we too are on the dreaded Caninsulin and she does seem to be settling down on it. The vet is happy to try other insulins if she can't settle in the long term - the cascade principle vets work on here means that they can prescribe "human" medicines if it is in the best interest of the animal. However, as I have found with Issey also having asthma, human drugs (she has a ventolin inhaler - the type the NHS hand out like confetti) and they cost an absolute fortune.
Applaws is pretty good, which you can get from Pets at Home - and they have an own-brand "deli" food which is very similar. Sainsburys do Encore cat food, which is again very low carb. The only problem is that these are not complete foods. The Applaws dry is about 15 per cent carb, which is not great, but the carbs come from potato, not grain, so is a slower-releasing carb.
Good luck!