If you need advice on the purchase or maintenance of a listed building you need an appropriately qualified and experienced Architect or Building Surveyor. These organisations maintain a register of individual conservation accredited professionals who have been assessed by their peers and whose accreditation is checked and renewed periodically.
CIAT Conservation Accreditation Register identifies Chartered Architectural Technologists competent in the conservation of historical buildings and their surroundings.
RICS or Royal Institute of Chartered Surveyors Building Conservation Accreditation
You may also be interested in SPAB
The SPAB believes old buildings have a future and takes a practical approach to their conservation. From cottages to castles and from churches to cathedrals the society is here to help buildings and the people who care for them.
Through SPAB's unique training schemes, courses, advice and research it helps people put its expertise into practice.