According to the Fourth Doctor, the Malicious Damage Act 1861 applied to lighthouses. He told Leela this after she had broken through the door to Reuben's room with a sledgehammer. (TV: Horror of Fang Rock)
Behind the scenes
The law is a real one and it probably could be applied to lighthouses. However, it does not appear to specifically mention lighthouses, only damage done to buildings in general.
