1. BPS conversion course
2. Work experience
3. Doctorate in clinical, educational or counselling psychology
4. Clinical neuropsychology masters (or the academic elements can be done by essay direct to the BPS)
5. Supervised experience
6. Send off details to BPS for accreditation
You're probably looking at 10+ years minimum to get to that stage, and I doubt there are many jobs as it is so specialised
Check out the BPS careers page for more info