Stately home Blenheim Palace is celebrating the 80th anniversary of its top secret wartime role as the headquarters of MI5.

In 1940, the Oxfordshire UNESCO World Heritage Site and birthplace of Sir Winston Churchill 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 outside the palace, the Great Hall was filled with filing cabinets and the Long Library became a typing pool.

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Part of the palace’s upper floor was also transformed into a communications centre, which included a translation service and reference library.

Oxford Mail:

Huts housing MI5 at the palace

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.

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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 to Blenheim where their passes were checked.

They were then transported up to the Palace, where they were checked a second time before heading into the Palace’s Great Court, through a third checkpoint.

“Everyone who worked at Blenheim Palace during this time was sworn to secrecy and, many of the staff, which were mostly women, did not speak about their vital roles to anyone,” said Blenheim Palace’s social historian Antonia Keaney.

Oxford Mail:

Queen Mary with the 10th Duke and Duchess of Marlborough

“We were fortunate enough to interview some of the ladies for an archive several years ago and some of them had only recently revealed what they did during the war to family and friends.

“One of the women said if the Germans had ever found out we had lost virtually every possible contact for their spies we would have undoubtedly lost the war.

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“For me it’s incredibly important to pay tribute to these extraordinary people and the crucial role they played in the war effort.

“What’s even more moving is how they kept their wartime secrets for so long and so well their contributions have been virtually overlooked for 80 years,” she added.

Oxford Mail:

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.

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“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 Ms Boot.

MI5 did not leave Blenheim immediately the war and the palace was not handed back to the Marlborough family until 1948.