Fifteen layers of trays, brimming with lettuces, salad leaves, basil and other herbs are growing underneath rows of multicoloured LED lights, stacked one above the other. The wall of edible greenery rises 10 metres high, all the way to the roof of a vast building in Lydney near Gloucester.

This vast matrix of glowing shelves is one of Britain’s latest vertical farms, growing plants indoors in a tightly controlled environment all year round. With the jump in energy prices and other costs, a string of similar ventures have gone out of business in recent years but the technology is still hailed by some as the future of food.

Operated by Jones Food Company (JFC), Lydney has moved firmly past the pilot phase to become a significant supermarket supplier. It supplies 30% of the UK’s cut basil, and can produce 550 tonnes of fresh greens a year.

Lettuces, pak choi, mizuna, komatsuna (known as Japanese spinach), watercress, basil, coriander, parsley and dill are grown at three times the speed of traditional horizontal agriculture. Salad crops take only 10 days – without pesticides, and requiring 94% less water. They are seeded on to a substrate of sheep’s wool and recycled plastic bottles using a method called hydroponics – growing plants without soil by feeding them mineral nutrient salts dissolved in water.

The site requires a lot of electricity to power the lights, heaters, humidifiers and other equipment but at the Lydney farm this is generated from renewable sources such as wind and solar, says the chief executive, James Lloyd-Jones, who set up JFC in 2017.

The business is backed by Ocado, with the online grocer selling its fresh salad leaves and herbs. Another customer is Asda, which sells an 80g homegrown mixed salad bag for £1. Meanwhile, the rival firm GrowUp Farms supplies its Unbeleafable salad range to Tesco to retail at £1.50 for a 90g bag, and its Fresh Leaf Co brand for £1 for a 70g bag in Iceland supermarkets, and has just launched in Spar stores.

Other ventures have fared less well. Among those that have gone out of business are the startup Agricool in suburban Paris in 2022, and last year, the Florida firm Kalera and the Kentucky-based AppHarvest, whose valuations had risen to more than $100m (£79m).

The biggest global player, New Jersey-based AeroFarms, backed by the Duke of Westminster’s property firm Grosvenor and Abu Dhabi Investment Office, had planned to go public with a $1.2bn valuation three years ago. It used a Chapter 11 bankruptcy filing to restructure its business in September. Germany’s Infarm shut its European operations, including its flagship farm in Bedford, to focus on “high-potential regions better suited for indoor farming, with low energy prices” such as the Middle East. And Growing Underground, which wanted to feed London greens grown in a former second world war air-raid shelter below Clapham High Street in south London, was dissolved in November.

The problems facing these companies were multiple: rising energy costs, the Covid-19 pandemic and cost of living crisis, trouble raising funds, and financial overreach.

“The bubble has burst; a lot of people have been burned by hype,” Lloyd-Jones says. “By setting up in the UK, we were never awash with cash or much help, and the UK has got very high food standards. And we also have to sell at a price that is quite low. So it’s made us a lot sharper in how we think and develop product ranges and pricing.”

The temperature in JFC’s growing room is kept to a constant 26C with 75% humidity, and the plants are swaying slightly as air is blown in through big blue sausage-like pipes. VNA (very narrow aisle) vehicles driven by humans zip down the lanes between the vertically stacked trays, bringing new seedlings and taking trays with fully grown plants away to be harvested, which is an automated process.

At its laboratory in Bristol, JFC has spent years perfecting the technology behind the growing room and adjacent germinating, harvesting and packing rooms. It uses robots as well as artificial intelligence, feeding data for temperature, humidity, nutrient levels and plant growth into a machine learning programme, to optimise plant cultivation.

Lloyd-Jones says: “We can export this technology around the world, like the Dutch exported their knowhow on greenhouses. The UK could lead in the export of this knowhow.”

The firm’s 56% shareholder Ocado, which builds warehouses with grids served by robots for retailers around the world, provides advice on automation. JFC, which employs 68 people, has developed a series of machines that move the trays of mature plants to be harvested and wash them afterwards. In giant black tanks, water – a mix of rainwater, mains supply and runoff from the plants – is topped up with nutrients and pumped into the growing room.

Aside from the new £23m farm in Lydney across 14,500 sq metres, JFC has a smaller farm in Scunthorpe that grows oak, hazel, alder and spruce tree saplings. The firm wants to open another vertical farm next year, followed by two to three more in 2026.

Another UK player, Fischer Farms, opened an even bigger, 25,000 sq metre vertical farm with £25m investment in the heart of Norfolk in November. GrowUp Farms, which employs almost 100 people, built its fourth vertical farm in 2022, Pepperness near Sandwich in Kent, next door to a bioenergy power station, using £100m funding led by Generate Capital, a US public benefit corporation that invests in sustainable agricultural infrastructure.

GrowUp was founded in 2012 by Kate Hofman and Tom Webster, who started with a shipping container and a greenhouse in a car park near London’s Borough market. Hofman tells of how they “cycled across London at 5am to deliver our first salads” to traders and restaurants.

“Pesticides, chlorine washing and travelling hundreds of miles all degrade the quality of the leaves,” she says. “We see vertical farming as part of the future of food. What we need is a resilient and robust food system. To create that, we need to be growing the right food in the right place, using the right technology.”

Floods, droughts and wildfires are “threatening traditional farming methods, meaning vertical farms will become a critical solution for a climate changed world”, says Stephan Dolezalek, who runs Grosvenor Food & AgTech.

JFC has its eyes on growing berries next, after experimenting with strawberries in its lab. But some industry experts are sceptical that vertical farming will ever be more than a niche.

Cindy van Rijswick, the global strategist for fresh produce and farm inputs at Rabobank, says: “The crops grown in these systems are not the main crops. Leafy greens are still a sort of premium product, not the bulk of the food market, and some of the more staple crops that people eat – grains, potatoes, rice – will never be economically viable to grow in vertical farms.”

It is more likely to work in the hotter countries. “With a lot of cheap solar energy generated in the desert, it could work in places like the Middle East, but in Europe, it’s more difficult. If you can make it work in the UK, it would be a great achievement because the European market is quite competitive,” she adds.

What is believed to be the world’s largest vertical farm, Bustanica, opened in Dubai last year with 30,000 sq metres of growing space, next to Dubai’s Al Maktoum International airport. It is owned by Emirates Crop One, a joint venture between Dubai’s Emirates Flight Catering and the US vertical farm specialist Crop One, and supplies airlines and restaurants.

Back at Lydney, Lloyd-Jones says: “If we built 94 farms of this size [Lydney], we could grow enough salad to replace those imported into the UK.

“I do believe that technology will provide food security in the future, however, not with herbs and salads. But you need to start somewhere … what we are doing now is creating supply security.”