Michael Portillo visits a top-secret Cold War stronghold, just a mile from the Cambridge campus where he spent his university years. The bunker, formerly known as RSG-4, was built in 1953 to house 300 local government officials from Cambridgeshire in the event of a nuclear attack. The former politician is also given access to the decommissioned Soviet nuclear submarine U-475 Black Widow - currently moored at Strood on the River Medway - revealing how close the world came to a full-scale nuclear war.

• Michael Portillo