Does anyone know the business use category for a therapy centre? Does it fall within B1a or is it D1

I'm about to take over an extisting therapy centre offering usual therapies - acupuncture, bowen, chiropractic, massage, homeopathy, counselling etc. We are due to move into new premises which is categorised for use as a B1a building. Does anyone know if therapy centres fall into this category or if they are another category - D1 for clinics and health centres seems most likely? How easy is it to change business use category? Thanks Jane