You had a low risk exposure. Heterosexual HIV transmission in the UK occurs mostly among immigrants from AIDS-endemic area, like southern Africa. Even among CSWs in London, only about 1 in 1,000 have HIV -- so the chance your partner had HIV is extremely low.
Therefore, from a strict risk-assessment perspective you didn't need HIV testing at all; the benefit of testing is purely from the psychological support you should be feeling from knowing for sure that you didn't catch it. In any case, the Duo test measures both evidence for the virus itself (specifically, the p24 antigen of HIV) and antibody, and a negative result on both of those at 4 weeks was 100% proof you weren't infected; the negative result at 6 weeks is superfluous. You definitely do not need any further testing.
I hope this helps. Best wishes-- HHH, MD
Thanks for your reply.
Your reply will help me clear it from my head which i have struggled with for the last 8 weeks.
Thanks again.