Gender ratio apparent? Yeah you notice it, but it also would be the case if you were doing a physics/engineering/computing course at any university. At other universities, arts and humanities courses balance it out so that the overall ratio is equal. Anyway, the proportion of female students has been slowly increasing.
Do students socialise? Of course they do.
Decent nightlife? Mate, it's London.
Life outside of uni work: yes. It does depend on how much work you actually choose to do. Inevitably there will come times when you do have to sacrifice going out to meet a project deadline or something. But not often, in my experience.