I've been here 10 years.
I work for a record company (
www.songphonic.com) and I used to work for Bronze records (Motorhead, Uriah Heep, etc.). I've played on record, or live, with Jeff Beck, Jack Bruce blah, blah, blah... I've been playing bass since 1977, and I'm studying the Double bass with a professor at the Royal College of Music...
Ok, enough of my background... let's talk about London!
IMO you will waste your time in London. There is very little work, and the majority of musicians are protective of the little work they've got. There are no venues that pay any money. Bands make an average of £120-200 IF you're lucky. There is a musical class system and "you are a foreigner" from the richest country in the world. Pub gigs are being taken over by karaoke machines and amateurs that will do it for free or damn near free. DJ's are more popular because they don't take up much space, not to mention that the pub will pay the DJ the same money they'd give a band. £150/1 or £150/4, it won't matter.
London will eat up your puny dollars mercilessly. It takes almost 2 dollars to equal 1 pound. My rent is £740 a month, and that's cheap for London. There has been an influx of Eastern Europeans and they are competing with everyone else for work, not to mention we are in the middle of terrorist activities. People are edgy, and the Muslim community here are feeling victimised. Not a helpful environment to say the least.
I'd done session work in Philly and had the recommendation of the engineer for Boyz 2 Men, Gerald Veasley, it didn't matter. I was going to auditions and being told "you're too good, you scared the artist" That translates into, "you're good, you'll probably want too much money." Remember, You are a foreigner, and an American. We're not very popular in the world right now.
Now for a positive note...
If you think like a businessman and not a bassist, you are doing yourself a favour. Playing bass is not enough IMO. Can you write songs? Can you read music? Can you sing? It's easier in Europe than here, as far as people being receptive, because I presume you'll come to London.. Everyone in Europe that have ambitions and fantasies come here.
If you're studying, I hope it's not that GIT, BIT bull****. That diploma is worthless against someone with gigging experience, an imagination, and that can write songs... BUT..., and I mean...BUT,
Maybe you'll come over, go to school and meet some like minded people, start a band and get a deal

DESPITE what I've said. If you feel in your heart it's something you have to do, DO IT!

but be prepared for the worst and hope for the best!