Huge place and we got free run of the whole site for over 5 hrs on a trip organised by SB.
A bit of history (copied from the official Drakelow tunnels website)
Drakelow Tunnels are spread over 285,000 square feet. Originally constructed for use by Rover in WWII under the Ministry of Aircraft Production’s Shadow Factory Scheme, the tunnels were mainly used for machine workshops and additional storage for Rover.
After WWII the tunnels got a second lease of life during the Cold War where the Government took control of the site as a Regional Seat of Government (RSG) in case of a nuclear attack. Less than a half of the site was converted for use during the Cold War period, where new rooms and equipment were installed.