MI5 at Blenheim Palace

This year marks 80 years since Blenheim Palace's role as the top secret headquarters of MI5.

The Story behind our Top Secret WWII Spy Role

In September 1940, Blenheim Palace became the temporary location of Britain’s secret intelligence agency, after its London offices were destroyed in the Blitz. A series of pre-fabricated huts were set up in the Great Court, the Great Hall was filled with filing cabinets and the Long Library became a typing pool. Part of the Palace’s upper floor was also transformed into a communications centre, which included a translation service and reference library.

As many of the records held in London had been lost, the work done at Blenheim to rebuild their intelligence documents was so vital to the country’s wartime role Churchill would call on virtually a daily basis to see how things were progressing. He reportedly also sent chocolates and cigars when specific projects were completed, and visited the site on at least one occasion.

Security surrounding the estate was extremely high and staff, who were mainly women and mostly staying at Keble College in Oxford were dropped off by bus at the Woodstock gate entrance where their passes were checked. They were then transported up to the Palace, where they were checked a second time before heading into the Great Court, through a third checkpoint.

MI5 did not leave Blenheim immediately the war ended as they had nowhere to go. The Palace was not officially handed back to the Marlborough family until 1948.

Spy Tours: Hidden secrets

Join a walking tour in the Great Court to discover some of the hidden secrets of Blenheim Palace, including the link to MI5 and Churchill. Find out more

MI5 Cynthia Boot

One of the last surviving former MI5 staff members is 95-year-old Cynthia Boot, who was just 17 at the time, and too young to join the forces. Even today very few people are aware of her secret wartime role.

“We had to sign the Official Secrets Act, and after that we never said where we worked, we always just said we worked near Oxford,” said Cynthia.

“We were allowed to say we were at the War Office, but we weren’t allowed to say what we did, what we saw, or how anything worked.

“We never said that we were in Blenheim but it was very precious to us because it was such a beautiful place to work,” she added.

The Ladies of MI5

Listen to the remarkable ladies of MI5 speak together for the first time in 2014 of their secret war.

The Ladies of MI5

Listen to the remarkable ladies of MI5 speak together for the first time in 2014 of their secret war.

Queen Mary with the 10th Duke and Duchess of Marlborough during her visit to the temporary MI5 HQ at Blenheim Palace in May 1944.