How about one of the museums or the zoo? They do pretty cool "lates" events for the public and could potentially come up with something excellent for a corporate event. Check out the websites for the Natural History, Science and V&A museums. I've also seen some very cool Zoo Lates events.
Are there any themes/common interests your guests would be likely to have?
All of the tourist attractions do this sort of thing - London dungeons, museums, sea life centre etc. I'm not sure how "cool" they are because they have been happening for years. The demographic you need to attract etc makes a big difference to what will work. I used to do this sort of work 20 years ago and one event that was super successful was a pie & mash evening, post of course but people like the heritage