For practices just keep asking around - I think many dont take under 18s but there are definitely those that do. You can use the RCVS Find A Vet search to help you find vets in your area. I would think chains like Vets4Pets would take work experience too.
Husbandry-wise, I don’t know of what’s in the Norwich area but try to get a mixture of e.g. lambing, dairy, kennels/cattery, and horse yard work. You might be able to find lambing placements via the NSA Lambing List or facebook groups such as The Lambing Club. Public farms/petting zoos can be a good shout too if there are any near you. There should also be stables around that you can get a couple of weeks at or some weekends helping out. There’s also quite a lot of pigs in East Anglia so maybe visiting a pig farm would be possible for you.
Generally, a polite email from yourself will suffice but you may need to phone up/visit places for a more direct answer or avoid being ghosted. Best of luck, it can be hard but just stay persistent!