Call your local council, ask them what you would need to do if you were to set up a business with people coming to your house for treatments.
Whilst registering is not a requirement in many places, some are stricter. Eg where I am currently I had someone at my door within days of starting monitoring how many people came in and out, business rates etc.
Just enquired about a couple of places I’ve thought of moving house to and the local authorities are just like..oh no we don’t care about that stuff. No registering, nothing. As long as you declare your tax with hmrc that’s all we care about. Dont even care about the planning permission! I was so gobsmacked. But never assume, get it in an email as evidence. Make notes of all the calls and what was said. You never know if you are talking to the right person and you can get penalised for it.
Also in terms of business rates, it’s only a business if you have more than 5-7 visitors per week. They will sit in a car and count people going in and out.