Thousands of online shoppers thought they had the bargain of the year after a glitch promoted the latest much-have device, out on Friday, for £49.99 in a pre-order.

The gadget normally retails at £659 for the 64GB Wi-Fi and 4G version.

As word spread on Facebook and Twitter, the Tesco website was besieged with savvy shoppers, many ordering several. One member of the site, Poker2009, fully embraced the deal, saying: “I have ordered 20.”

A Tesco spokeswoman said there was no way the deal would be honoured: “We always look to offer our customers unbeatable value but unfortunately this is an IT error, which is being corrected”

Retail experts said they expect a backlash from shoppers. When M&S refused to honour a pricing glitch in January, it was forced into a U-turn after thousands joined a web campaign.

In January, M&S offered 3D tellies worth £1,099 at a fifth of the price after an online blunder.

Initially, the retailer refused to honour the deal but eventually climbed down after thousands complained on via social media.

And last year T-Mobile offered free contracts by accident.

The latest iPad was unveiled last week and features a screen more detailed than a 40in HD TV. Huge queues are expected when the device goes on sale on Friday, starting at £359 for the basic 16GB Wi-Fi only version up to £659 for the top of the range 64GB Wi-Fi and 4G version.