One of the things we’ve experienced is that the cab fares double at Midnight (i think it’s midnight) which means that there are no cabs that will stop and give you a lift after 11:30 and before midnight. We ended up at a cab line at one of the tube stations, 20 cabs parked there at 11:45, every cabby out of the car talking to the others, until the rates change.
A friend mentioned that is worth hiring a car for the evening with a few friends, so that you have a ride home at the end of the night, but also you have a car to take you around if you want to find other events to check out.
From what i can tell, for the tube, if you get a 3 or 7 day pass (zone 1 and 2) was not that much more than the Oyster card as far as i can tell. But you sure want to avoid buying single trips during peak hours, you’ll pay £6 a day (3 day pass), vs £1.50 per ride with Oyster.