Hi, you could try the 'Outsiders Club' - http://www.outsiders.org.uk/club I have not had any contact with them but it might be helpful for your friend's service user to make more social contacts. It looks as though it is based in London. The website has lots of info on it. Its a shame that there aren't more organisations like Stars in the Sky as it is clearly a need for lots of people with Learning Disabilities. There used to be a group run at Harperbury Hospital but I think they have closed it now due to funding problems. But it might be worth giving Harperbury a call.
Also it depends from borough to borough about good social events that go on to give people the opportunity to make friends in a more 'normal' environment than structured services. I don't know if there is anyway to contact people on the forum privately, but if that is possible, please let me know where the service user is located and I might be able to let you know of some good groups and events.