It's difficult to give recomendations without knowing a bit more about your pal, in terms of how "high functioning" he is and particularly what types of girls he likes in real life - as you put it yourself plastic-big-tits-porno blondes and anime waifs are pretty far appart in terms of appearance.
Thanks Integral, I really appreciate the time and thought you've put into your reply. I might have to be a bit non-specific about him and who he likes as it could easily leave a trail of smarties that could identify him and/or me IRL, but, suffice to say, he's very high functioning, but afflicted with the social aspects of the condition.
What types of real girls does he like - are there any actresses / tv presenters that he fancies that can give us a steer?
His tastes are pretty conventional in as much as, like me, hes quite shallow in an aesthetic sense, so he probably wouldn't appreciate a BBW or a stretch-marked apron of flesh. But they're also diverse enough that I could imagine he'd go for a big-tit porno blonde
or an anime waif, as long as they fitted the bill with patience and some understanding.
You have actually disucssed this with your pal and aren't just planning on surprising him with a hooker one day are you ?? 
A good point, and yes, this is not something either one of us are taking lightly. We've operated on a traffic light type system and he knows he can put the stop light on any time. At the minute it's a flashing amber to proceed with caution, but he's also recognised that, if left to his own devices, he would probably never galvanise himself to take the plunge. Up until a couple of years ago, it wasn't something he had ever discussed, but, as he got older, it was clear that the loneliness was pushing him towards depression and frustration. The dating game - he believes - is a minefield even for someone without his condition, and you only have to watch an episode of The Undateables to see that rejection can hit some folks hard, which is a risk he's not really willing to take, and he also recognises that, with his condition, he might not be able to obtain anything like his idealised version of a sexual partner without paying for it.
I'm no expert on either Aspergers / ASD but I know that having as much of the punt be "controlled" as possible makes it more likely that your mate will be comfortable and enjoy himself - I'd guess that a familiar environement like an outcall to his home (although that comes with other problems) or a hotel he knows well would be better than an incall. Agreeing the perameters (in as much detail as you can) of the punt with the girl ahead of time will also by key. I'm assuming from your posts that you are an experienced punter yourself and know how to avoid the usual problems / potential issues.
I also think it would be very helpful if you were "on hand" in another room / hotel lobby to act as reasurance, depending on your mate's desires and need for support.
I think you are probably more expert on the matter than you give yourself credit for; these are all spot on considerations, and it's already agreed that I'll be "on hand" to either help him make a quick getaway if it goes tits-up, or to high five him if he comes out of it walking on air. I've got to admit that I'll be about as nervous as him going into it as there is scope for it to go wrong and, even if he doesn't blame me, I'll likely blame myself. But the alternative is what? Going his whole life like a Trappist Monk? Surely the guys on here are here because that's not a situation that they themselves want to reconcile to, so why should he?
I'm probably not the best bloke to give advice on London WG's, but there are two that I've seen this year that might be a good choice (both list "disabled clients" on their AW too): -
1) Lily Hart (External Link/Members Only or External Link/Members Only), very well reviewed, really adaptable and accomdating, and with the right makeup would look like an anime burd come to life. Also a friend of Violet below.
2) Parrma Violet (External Link/Members Only or External Link/Members Only) more buxom and alt/goth in appearance but would be really good at the reasurance / cuddle and chat side, and might have a personal background that would make her a good choice for a punter with Aspergers.
Your other option would be to approach HOD 1 or 2 and explain the situation (particularly try to speak to Cath the maid/madam) - they might be able to recomend a patient and understanding girl and might be happy with you "escorting" your mate and waiting on the premesis etc. This might help with the "controled environment" too.
Thanks; Lily Hart looks good so might pitch the idea to her if he likes the look of her profile too. HoD wasn't even something I'd considered as I thought it might be at the more impersonal end of the scale, but if you reckon there's some scope there then I'll give that some thought too. That's why I came here, asking for suggestions and, despite my bumpy start, I appreciate them all.
Also the TLC trust specialises in this sort of advice (I think they mainly focus on physical disabilities rather than cognitive ones), might be worth scanning their website (External Link/Members Only).
Already one step ahead of you on that one, but your thinking is spot on. Unfortunately that and another site which has a list of escorts who really are "disabled friendly" didn't really bear fruit. Unfortunately it seems like a lot of WGs on AW who tick that box on their profiles can't or won't put their mouth where the money is!
Best of luck! 
Thanks again, very decent of you.
