You could also try the UK Web Design Association. However you'll find that a lot of design studios either don't register with them or later request removal because of the hidious amount of spam received as a result of being in their directory.
Clook Internet - www.clook.net Fully managed UK based webhosting provider
Est 2002, 24/7 phone support, all the bells and whistles!
and just ask around for any designers needing work (from the UK). Or you can do that here too.
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