MI5 Talk

A daily talk at Blenheim Palace revealing how MI5 used the Palace as its secret wartime headquarters from 1940.

This daily talk explores MI5's move to Blenheim Palace in 1940, when the counter-espionage service — known only as Box 500 — made the Palace its headquarters until the end of the war. Visitors hear how the state rooms were converted for intelligence work, with the Long Library as a typing pool and the Great Hall filled with filing cabinets, and about the women bound by the Official Secrets Act who supported operations such as the Double Cross System ahead of D-Day. The talk also covers sites around the estate, including the Flagstaff Gate checkpoint, the Nissen huts of Great Court, secret trials on the lake and the Soviet agent among MI5's officers. No booking is needed; visitors simply gather at Great Court at 14.00.