Below Ross Davidson’s feet, the ground is sinking. But the boss of the Brogborough landfill, on the outskirts of Milton Keynes, isn’t worried that the ankle-deep mud will swallow him up.

It’s a gradual process. Every year, the largest repository of waste in western Europe sinks by about a metre as 25 years of binbag waste putrefies deep underground. Like a tray of tomatoes left out for too long, the 43m tonnes of accumulated muck breaks down into liquid, inorganic solids and methane gas.

Brogborough stopped taking waste a year ago and has since been covered with a thick layer of clay, but it will be decades before the decomposition runs its course. It is up to Davidson to keep the gurgling, seething mess under control. The black, foul-smelling liquid must be siphoned out constantly so that it doesn’t pollute the water table, and underground fires set off by chemical reactions must be smothered. Most importantly, the methane has to keep flowing because Brogborough, though it may not look it, is a gasfield.

More than 550 “wells” have been drilled into the site, their black plastic heads poking out from the mud and willowy grass. Each of them is linked to a central suction system that draws the gas generated by natural decomposition into an adjoining power station. The flow is enough to feed a line of gas-fired engines, two of which originally powered the QE2 across the Atlantic. They generate enough electricity to light 26,000 homes.

It is a set-up that any big power company would dream of. The site is big — 70 metres at its deepest point and covering an area equal to about 250 football pitches. This year it will generate about £18m in revenue for Infinis, the renewable-energy firm, but it costs only about £2m a year to maintain.

It helps that the fuel is free. Using current technology, there is enough gas underground to power the station for another decade at least. For Guy Hands, whose buyout firm Terra Firma owns the business, it’s easy money. Overall, Infinis, Britain’s biggest generator of power from so-called landfill gas, will pocket profits of £55m on £110m in revenue from the 80 sites it oversees around the country.

Yet there is a problem for the landfill business. It is dying. Owing to a combination of rocketing landfill taxes, an increasing aversion to burying garbage in these environment-conscious times, and generous subsidies for new technologies that convert rubbish into energy, Brogborough is the last of its breed.

An entirely new industry of high-tech metabolising plants and digestors is emerging to take its place. These sites are designed, essentially, to do what Brogborough does, but above ground and much quicker and more cleanly. “The great advantage of the new technologies is that instead of waiting for 40 years for this stuff to release its calorific value, we can get it in a week,” said Alan Lovell, head of Infinis.

By 2010, the amount of waste sent to landfill in the UK must be reduced by 25% from 1995 levels under the EU landfill directive. By 2013, it must be cut in half. This is a big challenge: in 2006 the UK sent 65m tonnes of waste to landfill, or more than a tonne per person. AMA Research, a consultancy, estimates that the UK will have to spend up to £30 billion to build the infrastructure to handle what, for decades, has been buried.

“In the past year there has been a sea change in the UK,” said Andy Street, head of SLR, Britain’s largest waste-energy consultancy. “When security of energy supply has become such an issue, it is sensible to get what we can out of waste. Waste isn’t waste. It’s a resource.”

Every year J Sainsbury dumps the equivalent of the Titanic into landfill — about 80,000 tonnes. Most of it, about 70,000 tonnes, is food waste such as ready meals, stale bread and spoilt fruit. By this summer, the supermarket giant expects to be sending no food waste to landfill.

It sounds ambitious, but Lawrence Christiansen, the supermarket giant’s green guru, has a plan. For the past five months Sainsbury has been testing a programme it plans to roll out across the company over the next two years. Instead of sending lorryloads of organic waste from its Northamptonshire distribution centre and 38 surrounding stores to landfill, the company has been trucking it to an anaerobic digestor operated by a small company called Biogen Greenfinch.

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