Think of farming, and the rolling fields of the countryside spring to mind. But across Britain's towns and cities, veggie growers, cheese-makers and honey producers are becoming established. Not since the Second World War, when people were urged to Dig for Victory, has urban farming been so popular.

Across the country, more than 2,000 new spaces for growing food have been created over the past three years. And this is just the start of the upsurge of inner-city farming. Already, eco-designers have been invited to look round the Olympic site in east London to see if there is potential for a farm after the Games.

While city allotments have long been popular, people are now growing produce to sell: Gordon Ramsay's Bread Street Kitchen features Bermondsey Frier cheese on its menu, while St Mungo's, the homeless shelter in south London, sells its vegetables to The Table Café in Southwark.

In Nottingham, Ecoworks runs a local vegetable scheme delivering vegetable boxes to eight points across the city, and in Newcastle, bees on the roof of Fenwick yield the honey sold in the department store.

Today, Sustain, the alliance for better food and farming, launches its report "A Growing Trade" to advise people how to grow for sale in an urban environment. Ben Reynolds, network director of Sustain, said: "In the last year, we have seen people start selling their urban agricultural produce."

In London, there are now almost 1,500 growing spaces that have joined Capital Growth, a scheme run by Sustain for city gardens and farms, funded by the Mayor of London. That has risen from only 50 at the launch of the scheme in 2008.

"It's a vast rise, with 50,000 people getting involved across these sites," Mr Reynolds said. "People are now thinking how to make this sustainable, and are establishing relationships with local restaurants. A growing number of community projects are going down the enterprise route."

Polly Higginson, author of the report, said: "There has been a real change in attitude in the community food sector towards how they see their pr ojects. Trading is a good opportunity to generate income to contribute towards project costs and to lift the ambitions of those involved."

Charlie Price is founder of Aquaponics UK, which nurtures plants and fish in symbiotic balance in urban locations, including the FARM: Shop in Dalston, north-east London. "Urban agriculture is evolving rapidly into a viable, cost-effective and engaging way to produce food in our towns and cities," he said. "It provides good quality, healthy food that is sustainable environmentally, socially and economically."

Andrew Merritt, co-director of Something & Son eco-design company, who devised the FARM: Shop, has already toured the Olympic site to look at potential spaces to make a farm after the Games.