I live in London too, but I lived in Lancaster for years. Despite its size, I loved the nightlife in Lancaster. You do see a lot of people you know, such is the curse of a smll city, but if you're more interested in meeting people always up for a laugh, getting involved with social circles who think outside the box, have regualr raves, house parties, guerilla gigs etc then its great. Aslo, when I lived in Lancaster we'd just hope on the train to Preston or Manchester and hit Gilly's Rock World or a gig at the arena or whatever.
Living in Lancaster is vastly different from London, but I miss what Lancaster has, being near to Manchester, Liverpool, Preston and also being able to run off for raves and secret parties in The Lake District and surrounding areas.
Its cheap, the people are mad as hatters and far more down to earth, laid back and up for al augh than in London and when there's no where to go we always just used it as an excuse to get everyone pissedo na house boat or raving in a field or jumping the train to Manc.
The train from Lancaster to Manchester Piccadily takes about 50 mins.