I was in London only once though but I think you should try all those romantic comedy which I believe tell the story that are closer to normal peole's life than the suspense and period movie. On top of my head now
1. Notting Hill
2. Love, actually (Have not seen but seemed to be flocked with British actors/actresses)
3. Sliding doors. (Gwyneth Paltrow goes British!)
4. Bridget Jones' diary and its sequel
5. Jamie Oliver's cooking series, particularly the later one that has more outdoor scene than the first one that he just cooked inside the studio.
I couldn't think of any British TV series that is fun to watch.
Also, I think Star World TV has some of the British talk show that one may get some thing and issue out of it if he can understand the accent...
In addition, reading British newspaper will help, particularly on the lifestyle section. Even better if you could even focus more on local newspaper on the exact area he will go. Unlike in the past, the internet should provide a cost effective access to such local news which I think is more important. Even the school newspaper, if they happen to have one, is one of the best thing to follow if you really want to know what's happening there.