The primary route into qualified social work is a degree. Previously, the main route was to obtain a DipSW (Diploma in Social Work) but this has been replaced by the new degree which requires, in addition to academic study, that all social work students must

"spend at least 200 days gaining required experience and learning… in at least two practice settings … working with at least two user groups, and have experience… of statutory social work tasks involving legal interventions."

The best place to start is to look at the General Social Care Council website

http://www.gscc.org.uk/