Therapists are not obliged to carry a first aid kit. If you're not a qualified first aider, then you shouldn't do first aid as a therapist, i.e. in the workplace. But there's nothing stopping you from doing the basic HSE first aid at work course, and then you will know what you need to carry and what you can do, etc.
I do my first aid qualification with St John's and have to requalify every 3 years.
HTH,
Myarka.