To work as a state-registered music therapist, you need to complete a postgraduate course accredited by the Association of Professional Music Therapists (APMT) and recognised by the Health Professions Council (HPC).
See the APMT and HPC websites for details of approved courses.
To get onto a postgraduate diploma or Masters in Music Therapy, you will usually need to have completed a three-year diploma or graduateship from a college of music, or a degree in music from a university. You may also be accepted on to an accredited postgraduate course with a degree such as education or psychology, as long as you have a high standard of musical ability - check with colleges or universities for exact entry requirements.
Many institutions will also expect you to have experience of working with children, people with mental health issues or learning disabilities. You should contact the voluntary services coordinator at your local NHS Trust for information on voluntary opportunities.
With some NHS Trusts, you could start out as an assistant therapist. For this role, you may not need any qualifications, but relevant paid or voluntary experience would be useful (check NHS Jobs for vacancies). You may have an advantage if you have a background in an area such as teaching, community or social work. A career as a professional musician would also be helpful.