Fwiw I'm a londoner and a long time drinker

and there is definitely big opportunities.
I think OP is going a bit extreme, but as a couple of suggestions:
- when I was in holiday in Bermuda we went to a beer pong night. It attracted hot american girls and there are tons of american girls in London who would love this, which in turn attracts all the guys.
- Another idea is trying to set up a chain of bars that are open till late, like 3am, but don't play loud music. Trying to find somewhere like this in London is never easy. Also if you knew you'd always get served within 1 minute this would be a huge plus. I am always amazed how some bars are so slow, whilst I do prefer pints if they sold reasonably priced bottled beer they could speed up the service so much. Also nothing worse than being stuck behind someone who orders 4 different cocktails
edit: regular drinkers in London around my age (late 20s) would be up for some different nights out, esp helpful for birthdays etc, for example one night a week could be beer pong, one night a week could be olympics night where you do challenges etc, idk, just a thought