We haven't managed to convert our loft but we had a quote from (and will eventually use) Roof Top Rooms (www.rooftoprooms.co.uk) who were recommended by a few friends who have lovely loft conversions.
I also know lots of local people have very happily used Pat, Another Level (http://www.loft-conversion-specialist.co.uk).
I believe you tried to contact us today by email. Unfortunately we are having trouble responding to your email address. Could you please send your number to us or call us on 01279654716.
Herts and Essex Lofts
Hi, we used Bracken Lofts, a small company (2 brothers) who we can totally recommend. Very professional, hard working, and tidy, and they did a fantastic job, particularly on the staircase, which looks as if it has always been part of our house (well it would, if we'd got round to carpeting it!) You're welcome to come and see our conversion if you like (we're in Tancred Road).