Bletchley Park Post Office has an incredible history. Built as a Butler’s Quarters in 1900, when the codebreaking centre was a private estate, they were used for top-secret mail at the start of World War II, complete with undercover post box numbers and deceptive diversions through local department stores.

After hostilities ended, the rooms became a sub-post office for thousands on training courses at the park, and during the 1990s it became a “gift shop”, pleasing collectors with hundreds of first day covers, starting with the 50th anniversary of the D-Day landings and going on to celebrate the Battle of Britain Memorial Flight and The Royal British Region.

Now the office has been refurbished as a place where visitors can make postcards and “secret” mail packs, sent from a mock-up wartime post office.

Michael Sefi, the Keeper of the astonishing Royal Philatelic Collection at St James’s Palace and an advisor to the Queen since 2003, unveiled the latest guise of this modest corner of Bletchley. It’s the latest twist in the tale of a tardis worth discovering.