I can definitely recommend Ruth Weighill of Forkful Food.
Ruth has provided canapés etc for a couple of big parties I've held - and the food and service is first class, she knows what she's doing.
Ruth lives on the Magdalen estate and can be contacted here;
http://www.forkfulfood.com/
Also I'd like to say I used Forkful on a personal basis - not business related!