I would recommend Sarah Marshall, who is the architect doing our extension and is great. Sarah is part of hales marshall design architects ltd, t: +44 (0) 20 8761 0050, w: www.hmda.co.uk
We have used Minns and Langton for a number of projects on our home, and found them excellent. Am sure they could do what you're after. www.minnslangton.com has contact details for Nick.