BBC employees were offered the chance to survive a nuclear holocaust by broadcasting from an underground bunker, but they could not tell their wives, newly released files reveal.

The broadcaster secretly drew up plans during the Cold War for how it would run a Wartime Broadcasting System in the event of a major disaster.

Early versions of the plan - known as the 'War Book' - say that staff were "assigned" or "designated" to go underground, but later editions suggest they were “invited”.