I'm not aware of any attempt to 'sue' going on - as far as I know he has simply made an appeal against the decision to allow him the surgery, but I've only read the BBC account:
BBC News - Man appeals for NHS gastric bypass surgery, there might be other info but I haven't read it.
From what I can gather the usual BMI for weight loss surgery is 40 (his is 43) or lower "if they have other serious medical conditions" (which he does), but his PCT has set a higher limit of 50 (presumably to cut costs), which to be fair is treating people unequally and could be seen as a breach of his human rights (although this doesn't seem to be where he has brought human rights into the argument - that seems to be the right to a family life). Where he lives has absolutely no relevance to whether he is in need of treatment, we should all be treated equally.
He also says "even an extremely calorie-restricted diet has failed to help him lose weight" - that doesn't necessarily mean that even on minimal calories he isn't losing weight (and therefore bariatric surgery woudlnt work) - it might mean that (for whatever reason) he isn't able to stick to manage such a diet. (Realistically, how many of us on here stick to plan 100%? Its not easy and lots of people out there have many problems, physical and mental, that might make it difficult or imposible to do so - without knowing this guy we can't judge him. Maybe he is being out of order but he sounds pretty desperate to be doing this.
Sorry if Im repeating what others have said, this thread is filing up with replies faster than I can write...