Today the subterranean bunker is a source of intrigue for amateur explorers, who have documented visits on YouTube and websites dedicated to derelict underground finds.

Built into a bank in the forest, its foreboding entrance leads down into an H-shaped bunker with reinforced concrete walls — a departure from the corrugated iron sheets typical of traditional air raid shelters.

Sensible wartime planners installed a vertical escape shaft at the far end, which is now inaccessible thanks to a broken ladder and large tree root.

It would have been constructed using a cut and cover technique, with the structure of the tunnels built within an excavated site and then covered with the backfill material.

Though it’s certainly no billionaire’s bunker, there is suggestion that the shelter has direct links to one of the most dramatic passages in British military history.

It is believed to have served nearby Brooklands, a motor racing circuit and aerodrome that was turned over to the production of military aircraft during the Second World War.