Food of the future: London air raid shelter to underground farm

Vertical farming, production of crops in a series of stacked levels, is a fast-growing industry with billions of dollars being pumped into projects across the globe.

In an underground World War Two air raid shelter where London tube trains can be heard rattling overhead, aromatic coriander leaves tilt towards the pink glow of LED bulbs - a vision of how farms could look in the future.

Zero Carbon Farms grows herbs and salads in Clapham, south London, a densely populated area with no room for conventional agriculture. But 30 metres below ground there is a kilometre of tunnels, and technology has made farming here a reality.

Seven years after its first harvest, the company will soon double its growing space, responding to strong demand for its peashoots, rocket and watercress from major British retailers like Marks & Spencer and local restaurants.

Buyers like the freshness of the produce, which can make it onto a diner's plate within two hours of harvesting, as well as its arrival into the city without racking up emissions by air or from a long journey.

"The future is very, very bright for this industry and I think that what really is going to be the fundamental pivot point is the right application of technology," said the farm's head grower Tommaso Vermeir.

Vertical farming, the name given to the production of crops in a series of stacked levels, often in a controlled environment, is a fast-growing industry with billions of dollars being pumped into projects across the globe.

It is seen as part of the solution to the food security challenge posed by population expansion at a time when climate change and geopolitics threaten supply.