E-Cube

It is made of wax, is barely three inches across and comes in any colour you like, as long as it's black. And it could save more greenhouse gas emissions than taxes on gas guzzling cars, low energy light bulbs and wind turbines on houses combined. It is the e-cube, and it is coming soon to a fridge near you.

Invented by British engineers, the £25 gadget significantly reduces the amount of energy used by fridges and freezers, which are estimated to consume about a fifth of all domestic electricity in the UK. If one was fitted to each of the 87 million refrigeration units in Britain, carbon dioxide emissions would fall by more than 2 million tonnes a year.

The patented cube mimics food and is designed to fit around a fridge's temperature sensor, which usually measures the temperature of the circulating air.

Because air heats up much more quickly than yoghurt, milk or whatever else is stored inside, this makes the fridge work harder than necessary. With the cube fitted, the fridge responds only to the temperature of the food, which means it clicks on and off less often as the door is open and closed.

Trials are under way with supermarkets, breweries and hotels. One of the largest, the Riverbank Park Plaza hotel in London, fitted the device to each of the hotel's 140 major fridges and freezers. David Bell, chief engineer, says energy use decreased by about 30% on average - enough to slash the hotel's annual electricity bill by £17,000. The Park Plaza group plans to fit them throughout its UK hotels, and to recommend them overseas.