1) You will need a 3-year degree in Psychology that the British Psychological Society accredits. This gives you a GBC (Graduate Basis for Chartered Membership of BPS).
2) You will need to complete an accredited Doctorate in Social Psychology because it prepares graduates to be an independent researcher in the area. Accomplishment of a Doctorate will lead to eligibility as a Chartered Psychologist.
Graduate Basis for Chartered Membership of BPS - Basic requirement for postgraduate study in Psychology