YES!!
First off:
The Bass Gallery in Camden
www.thebassgallery.com. You should visit Camden if you're in London anyway, you may as well take a trip to a bass shop whilst you're there. Great selection of basses and very friendly staff. They also make great custom instruments, do a quick search for Sei Bass on TB.
Secondly:
The bass centre in liverpool street
http://www.basscentre.com/cat/index.php MASSIVE selection of bass goodies, go and check them out.
Also:
Denmark Street! It's a street full of guitar shops, it's a bit pricey down there and staff in the shops have a bit of a reputation for being rude/abrupt but it's worth going down there for the history, and great selection of vintage intruments. There's one bass specialist called the Bass Cellar, but most other shops have basses too.
Sound Control. Englands version of guitar centre, they're the only shop that stock Schecters in the UK and they usually have a good selection of Fenders and Warwicks. Don't pay full price in there though, they'll always move on price.
That's where I'd start, but I'm likely to have missed some out maybe try a quick search on google?
[EDIT]
To get to denmark street: Tube to Tottenham Court Road, take exit towards Charing Cross Rd (signposted) Walk up CharingX Road, past astoria Denmark Street is second on Left.
Sound control: Off af Tottenham Court Road tube, turn on to Oxford street, Go in to Virgin Megastores and it's in the Basement.
