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An abandoned World War 2 bomb shelter, deep below the busy streets of London, may not seem like the ideal place to set up a farm. But that's exactly what a team here has done, using modern hydroponic farming methods and the latest LED technology.

Run by Growing Underground (part of the Zero Carbon Food company), the project aims to grow crops in the most environmentally friendly way possible. The water for the crops is on a constantly recycled circuit and the tunnels remain at a constant temperature so don't need to be heated.

The closed environment of the tunnels also means pests aren't a problem, which in turn means that no pesticides are required. And thanks to the farm's location, there's minimal travelling required for the crops to reach restaurants across London.

The farm is both a proof of concept -- showing that food can be grown in what seems like such a hostile environment -- and a commercial business. Various restaurants take deliveries from Growing Underground and top chef Michel Roux Jr is on the company's board.

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Far removed from the rolling hills and wide skies of typical farmland, this farm is housed 100 feet (30 metres) below ground.

The bomb shelter was built in World War 2 and at peak capacity was able to keep 8,000 people relatively safe from the devastation in the streets above.

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Instead of beds of soil, the crops are grown using hydroponics, where they grow in water. The plants only require a small amount of material for the roots to grip on to -- in this case, recycled rugs -- and are fed a precise amount of nutrients through a carefully monitored water system.

It uses a system known as "ebb and flow" in which the whole bed fills with nutrient-rich water that then slowly drains out, ensuring the plants get the food they need but aren't left standing in stagnant water.

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Most of London's shelters are dotted along the Northern Line -- the farm itself regularly rumbles as tube trains pass overhead. The majority of shelters are accessed through stations, but the farm has its own dedicated entrance, so the team doesn't have to battle their way through ticket barriers carrying supplies every day.

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There's no natural sunlight of course, so the lab is rigged up with a host of LED lights.

The constant conditions in both light and the 16C (61F) temperature means that crops can be grown all year round. Traditional horticulture can at times be difficult as often unpredictable weather patterns -- in part a product of climate change -- means that crops can be easily lost.

The Growing Underground team are able to constantly monitor their plants to ensure conditions are always optimal. Many of their plants are able to go from seeds to being harvested in 10-15 days and can achieve several crops in a month -- both quicker and more reliable than traditional farming methods.

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The LEDs are specifically designed for commercial farming use and don't come cheap. Various types of bulbs are being tested to see which ones give the most natural equivalent light for the plants.

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Different LEDs have different wavelengths and that can change how the plants respond. Some radishes grew with a darker colour under some lights, for example.

Does growing under LEDs, rather than natural sunlight, result in lower nutritional values from the crops? Not according to farm manager Gabriel De Franco, who explains that micro crops such as these already have higher nutritional value than their larger counterparts and are higher in antioxidants.

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Various types of plants are being grown in the tunnels, including rocket, mustard, coriander and Thai basil.

Growing Underground promises that no crops will be delivered outside of the M25 motorway that encircles London. The travelling would not only have a carbon impact on the environment, but detract from the freshness of their products. Growing Underground claims its crops can be picked and delivered to the kitchens in only four hours.

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All crops are being grown in their micro forms, as full-sized plants would require deep beds for their roots. Many of them, therefore, look like rather less interesting watercress.

I had a taste of the coriander and mustard plants. The flavours were intense, but not overpowering. Their size of course means they won't be the main event in any meal, but will be used to add fresh flavours.

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Team members will spend up to three hours a day down here. I asked if they've ever driven go-karts in the tunnels. They hadn't.

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It's easiest to think of the lab as a greenhouse built inside the tunnel. It's sectioned off from the grubby surroundings by polythene walls.

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The lights are all extremely low-energy LED bulbs, so don't cost much to run.

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During the trial phases, the crops have been sectioned into these squares in order to ascertain the best density at which to plant the seeds.

More dense planting means more crops, but it will restrict the amount of light each plant receives, which could affect the quality, so there's a fine balance.

Once the density has been figured out, the whole bed will be used for planting.

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Marching down this long tunnel is made all the more creepy by the glowing pink of the lab at the end.

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Does your office look like this? I kind of wish mine did.

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This is the machine that's responsible for pumping the water around the plants.

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I assume this is fine.

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The water is constantly recycled and treated with various filters to make sure it's of good enough quality for the plants.

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A massive fan sucks air out of the lab, while another one pushes more back in. The circulation helps keep the air within fresh, which the plants appreciate.

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This is the entrance to the tunnels. Not exactly glamorous, is it?

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And here's the team's office.

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I entered the tunnels via a seemingly unending spiral staircase.

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I had to step through a chemical wash to make sure my feet didn't bring in any germs or bugs.

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This currently unused room at some point will be turned into a decontamination area for when large groups like school classes visit.

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Even deeper into the Earth's crust is where you'll find pumps that pump up rain water that's filtered down through the rock.

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Although using completely organic techniques, the food can't be officially certified as organic as only crops grown above ground qualify. This may be changed as underground farming becomes a more common practice.

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This is a different type of hydroponics system. It's called the Nutrient Film Technique, or NFT for short.

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There's no soil for the plants. Instead, their roots are able to spread into these troughs, along which a thin film of water, packed with the correct nutrients flows.

It's apparently a difficult system to get right. "Get it right and the yields are amazing," farm manager Gabriel De Franco told me. "Get it wrong, you'll lose your whole crop."

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These are the plans for the underground network. You'd be forgiven for thinking they're props from a heist movie.

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At the moment, there's a single layer of plant beds, but expansion plans will see the beds stacked three high.

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Being 6 foot 2, it wasn't easy for me to squeeze under this beam in the entranceway. Which is why I smashed my head on it. The things I do for stories, eh?

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Growing Underground leases the tunnels from Transport for London, the city's transit authority. Only a small section is currently used for growing, but the team hopes to expand along the tunnels with future investment.

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Apparantly the plants love the vivid pink light given off by these LEDs.

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These lights have a slightly more neutral tone, but the team is still in the process of testing which lights are better for each type of plant.

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You'd need to eat a lot of micro crops if you planned to live off them alone.

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There's around 10,000 square metres (100,000 square feet) of space available down in the tunnels, so there's plenty of growing space.

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The tunnels are all drilled as round tubes, so the flat surfaces you walk on are mostly false floors. Beneath those floors is the other half of the tube, which would make perfect storage space for a larger farming project. Or, as I suggested, a skateboard half pipe.

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These are some of the original fuseboxes, long since out of use. Some of them are more modern.

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There's a cool breeze down here, due to the vents that link it to the surface.

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