How much spending money will I need for a hen night in london?

Question

Going on a friday afternoon, coming back on the sunday. so two nights in the city centre (flights and hotel are booked and paid for) how much are drinks? if I spend £50 on a night out in glasgow will that last me past 10pm in london? I'm assuming I'll stay away from the shops! Might try and book a show, how much are they, are food/drink expensive in there? please help!