the erection of any additional building within the curtilage of another building (whether by virtue of Class B or otherwise) and used in connection with it is to be treated as the extension of that building, and the additional building is not to be treated as an original building;

where 2 or more original buildings are within the same curtilage and are used for the same operational purposes, they are to be treated as a single original building in making any measurement; and

“employee facilities” means social, care or recreational facilities provided for employees or servants of the Crown, including crèche facilities provided for the children of such employees or servants.