Borthwick used his islet off the coast of Spain to spy on that country’s marine activities in what
The Times describe as “a little-known episode of the First World War .” Jacqueline Sorel, an Anglo-Dutch author who is writing a book about Borthwick’s life, says Borthwick came under the command of Lieutenant Colonel Charles Thoroton, the Gibraltar-based chief of British naval intelligence for the region. His task was to gather information pertaining to the movements of German submarines, and to identify secret fuel depots.
Sorel told The Times that the diary was written by another member of Borthwick’s “British spy ring,” a gentleman by the name of George Lee Boag, who was the British manager of the Great South of Spain Railway. The diary is currently owned by Alison Matheson, Boag’s great-niece, and it refers to Borthwick’s control of covert operations in the Almeria province . Furthermore, an entry made in 1916 says Borthwick was called on to discus