Retailers are bombarding shoppers with promises of Black Friday deals, but experts warn a healthy dose of 'buyer beware' is in order.

Amazon.co.uk has already started with the deals, promising that more than 7,000 will be on offer this week on items ranging from Acer Notebooks to Minions toys and Woody Allen boxsets.

It claims deals will see current prices cut by an average of more than 40%, saving customers tens of millions of pounds on popular Christmas presents such as Xbox and Nintendo consoles, watches and electric toothbrushes.

Ebay is expecting nine million Britons to visit its website over Black Friday and will be unveiling new deals every morning at 8am this week and through the weekend until Monday.

John Lewis has launched its Black Friday website and has promised to honour its Never Knowingly Undersold pledge and match its competitors' prices.

Halfords will be offering children's bikes at up to half price from Friday through Monday, and BT is offering a range of deals on its broadband, TV and mobile offers.

Argos and Currys PC World are just two others to have launched pre-Black Friday offers, promising to reveal more on the day itself.

But Martin Lewis, founder of MoneySavingExpert.com, warned that the majority of Black Friday deals "aren't special" and advised shoppers to cross-check deals with items they actually need.

He said the only difference over the last few years, despite the hype around Black Friday, was that all the codes and vouchers offered by retailers in November and December were crammed into one long deals weekend.

Mr Lewis said: "There are, of course, the much-hyped huge discounts of single items like giant TVs. Yet the stock on these is so limited, they're far more akin to competitions than offers. With thousands of people trying to get them, it's a lottery.

"The real boon of Black Friday, Cyber Monday and the rest of the Christmas shopping deals and codes is that if you have a specific list of things you plan to buy, if the store that sells them has a cross store discount code, that's the moment to pounce.

"Above all, remember, if you don't want something, don't need it or can't afford it, then don't buy it."