Hello! I can’t speak to sex therapists in London, but I’ll say that we get a ton of people in the UK in these forums so doing a search for “London” might turn something up. You may also find something useful recommended in this thread:
http://mazewomenshealth.com/forums/topic/london-botox/
I didn’t have sex therapy as part of my treatment (I did the botox method) but I do know that vaginismus is very linked to the emotional side of the problem (stress, pain, anxiety, low self-esteem) so treating the root emotional causes even through regular therapy can be hugely helpful. I got some of that at the Maze Clinic and I wouldn’t have made progress without it! I hope you get some good suggestions from fellow forum users!