SWFounders meetup in Bristol is a good place to start http://www.meetup.com/sw-founders/. It seems to attract a couple senior devs looking for an opportunity when I've been there.
Secondly, feel free to drop me an email (freebananas at gmail). I run http://www.meetup.com/Bristol-and-area-CTO-meetup/. If you can give me some more details I occasionally find out if someone is looking for something.