Not that the Soviets had any idea where it was. It's not as if the locals thought it was strange and interesting, and hiding it under one of the biggest military bases in the country, and a prime first strike target, was a work of Whitehall genius.

Civil servants were expected to travel to the location by train, having been given standard tickets - which meant they'd very likely have been waiting at Paddington while the bombs were going off.

You can go for a virtual drive around the bunker here.