Around London, there are eight deep-level bomb shelters built during World War II. The Clapham North shelter, constructed between November 1940 and 1942 at one point housed 8,000 troops in the labyrinth of stairwells, parallel tunnels each measuring 16 feet six inches in diameter and 1,200 feet long, buried over 100 feet underground.

The Clapham South shelter in 1948 was used to house 200 of the first immigrants from the West Indies who had arrived on the MV Empire Windrush for four weeks until they found their own accommodation. Even more surprising in 1951, it became the Festival Hotel providing cheap stay for visitors to the Festival of Britain.

On 21 May 1956 serendipitously a fire at the Goodge Street shelter coincided with Parliamentary consideration of a Government Bill seeking power to take over the shelters, subsequently the Minister of Works assured the Commons they would not again be used for human occupation in peacetime.

So what to do now with these miles of tunnels? Some are now used to store documents, but at the Clapham South shelter, the world’s first underground farm can be found.

Growing Underground uses LED lights that bathe the bunker in an eerie pink glow. The lights shine the brightest at night when electricity is the cheapest. The produce is grown with hydroponics, meaning the seeds rely on a cocktail of mineral nutrients and a water solvent rather than soil. Varieties of coriander, broccoli, fennel, and other micro herbs are produced to promote zero-carbon food. The 550-square-metre area fitted with hydroponics produces about 20 tonnes of greens every year.

The company now offers tours to the public, allowing visitors to tour the eerie pink farm of the future deep below the buzzing city streets and take home micro herb salad harvested straight from the farm.