NATIONAL FEDERATION OF ROOFING CONTRACTORS
The NFRC is the trade association for the whole of the roofing industry and have a very useful website with a list of all reputable roofing companies in your area all searchable by postcode. They also have a large library of helpful publications as well as knowledgeable staff to help with any roofing based question. Any company you choose that is a member of the NFRC must carry out works to national standards or risk their membership.