Microwaves in Britain generate as much carbon dioxide as more than one million cars, scientists have concluded as they call on people to use the ovens more efficiently.

Scientists arrived at the figure after studying the broad environmental impact of microwaves, taking account of their manufacture, use, and end-of-life disposal.

There are around 23 million microwaves in homes across the UK, but despite their huge popularity, little is known about the effect of the devices on the environment, said the researchers.

The University of Manchester team found that the ovens generate around 1.2 million tonnes of carbon dioxide each year, the equivalent to 1.3 million cars.

On average, a single microwave uses 573 kilowatt hours of electricity over a lifetime of eight years, which compares with a seven watt LED light bulb being left on continuously for almost nine years.

The study’s authors suggest consumers should use microwaves more efficiently by sticking to cooking instructions rather than just guessing, or always using the highest setting.

Lead researcher Dr Alejandro Gallego-Schmid, from the university's School of Chemical Engineering and Analytical Science, said: “Given that microwaves account for the largest percentage of sales of all type of ovens in the EU, it is increasingly important to start addressing their impact on resource use and end-of-life waste.”