I was thinking along the tube lines (if you'll excuse the inadvertent pun) too. I was thinking on a smaller scale though, and using one of the several disused stations. Overnight would be cool, and would mean all live areas could be used as the current could be isolated. I think the current can be separately isolated on some of the outlying disused stations that don't see through traffic anyway, allowing for day games.
Of course, the training course you have to do to be allowed underground might be an issue, though you might be able to get some kind of exemption.
Not sure how they'd feel about a load of BB's rolling around the place either.
Either that or some of the old military tunnels from WW2. There are a load under Chancery Lane in London, and there is a big network in Rochester. Those would be great for milsim with period clothing and weapons. I seem to remember there's a fairly extensive tunnel network at Dover too?
Or for that extra special day (and I can actually see this coming off) Fort Boyard! Sadly I don't think we'd get Melinda, but the fort would make for some great CQB!
