Supermarket Asda has launched a gadget trade-in service that allows Brits to get cash for their old technology.

Web users can find out online what their technology is worth and then using the Freepost enevelope sent to them (they'll also be able to pick one up directly from stores from June) they can send their device off to Asda, in return for a cheque or bank transfer for the value quoted online.

At present the Asda Tech Trade-In service is available for mobile phones, satnavs, digital cameras, MP3 players and portable games consoles. However, from June, the supermarket plans to expand the trade-in scheme to include laptops, tablets, games consoles and other large electrical goods.

Furthermore, the supermarket is offering a "we will not be beaten on price" pledge, which means if a consumer is offered more for their gadget for any one of the specified rival trade-in schemes, including Envirofone, Mazuma, Sainsbury's, Tesco and Boots, Asda will pay the difference.

Research by Asda revealed there could be as many as 35 million unused old mobile phones in the UK, which amounts to an estimated trade-in value of £700m. The supermarket also calculates there are 11 million old unused digital cameras, nine million old PCs, 5.5 million old laptops and more than a million redundant Sat Navs in UK homes.

"We reckon that the average UK home has hundreds of pounds worth of old gadgets that could be traded in for cash. There are more mobile phones in the UK than people, for example, so there is a lot of cash out there waiting to be released," said Phil Stout, Asda's Electronics Service Manager.

"Our tech trade-in service means customers can now save even more on their gadget purchases at Asda or use the bounty to save on the cost of day-to-day living."