Any Advice for Starting a Career in Rehab / Dependancy Clinic?

I live in the UK. I am looking for a career change, I would really like to work in a rehab centre or dependancy clinic.

Do I need any formal qualifications? Would I need to volunteer somewhere first? If I would need either of these how would I go about this?

Also, do you think it would work for or against me if I have some experience of the affects of drugs myself?

Thanks for your help.