Well, I feel like browsing, so I thought it would be nice to compile a list of the various online shops selling vintage and used basses in the UK, or indeed the EU. I'll add your suggestions to the original post. Here's the list so far, in alphabetical order:
The British Isles:
Absolute Music (Bournemouth)
Andy Baxter (London)
AngelDust (Multi-location?)
Bass Direct (Warwick/Leamington Spa)
The Bass Gallery (London)
Charlie Chandler's Guitar Experience (