well if you get an education visa to train Muay Thai. You’re going to be stuck at that gym because your visa will be attached to the gym. So you’ll have spent 2-3k GBP and could get stuck with poor training. It’s better to join a language school and get your ED visa through them. So you can spend a few weeks/months at a gym before deciding if you want to stay there long term
Don’t get an education visa for Muay Thai get an education for Thai language instead. The schools that offer the ED visa for MT aren’t usually the best or might not be suited to you. There are many great gyms in Phuket you’ll want to spend some time trying a few - I personally recommend
As Rob has said above it’s much better to get an education visa to study Thai language and spend a couple of hours each week doing that. The gyms that provide education visas are not the best. If you want the best Muay Thai training go to a proper Thai gym and not a tourist gym.