The qualifications needed to work at a centre will vary from centre to centre, therefore, it is a good idea to speak to your local service and get some guidance from them.
However:
In terms of supported contact centres – no qualifications are needed. The people running the service will provide all the training you need.
To work as a contact supervisor in a supervised centre, you will ideally have an NVQ L3 in Health and Social Care (or equivalent).
To work as a co-ordinator or manager of a supervised centre, you will ideally be a social worker, or similar professional.