Udayana, I didn't note whether or not the man had his treatment on NHS, presume he did as he was in prison.
No I don't think he should sue but I don't know every fact.
Doctors can only do so much there will always be some who later regret the change however convinced they are at the time that it is right. I read of a case a few years ago of a man who was so heartbroken, depressed and demoralised after his marriage broke up (more to it than that but that was trigger), that he had gender reassignment and later wanted to change back, butcases like those are in the minority.
Maybe there should be more safeguards?