Owners of listed buildings need to be particularly careful in how they maintain, alter and extend them. Conservation of historic buildings is specialist work requiring professional guidance. Most works of alteration to listed buildings requires consent of the local planning authority. This is not always as straight forward as it may sound and professional advice could be of benefit. There may be some good news with regards to VAT for some owners of listed buildings.
If your building is within a Conservation Area, you may require Conservation Area Consent for external alterations which change the appearance.