Hi there,
Although not local, Jane at Lily Matthews
www.lilymatthews.co.uk is great. She has made beautiful roman blinds for our flat in Earl's Court before we moved and more recently for our house in Balham and we have been really pleased with her work.
She operates out of Tenterden in Kent but can pop up to London for jobs where required. Her prices are very reasonable when compared with London equivalent so even when you factor in a travel cost it can still work out cheaper depending on what you are after. It might be worth dropping her an email or giving her a call.
Hope that helps!