Nearly nine in 10 products sold on Black Friday are available for the same price or cheaper earlier in the year, according to consumer group Which?. It urged consumers to “do some research” in order to spot genuine bargains during the 27 November sale.

Retailers including Amazon, Argos and John Lewis said they offered good deals all year round, not just during seasonal shopping events.

Natalie Hitchins, head of home products and services at Which?, said: “Deals that look too good to be true often are, so don’t fall for time-limited offers and if you are looking for something in particular, do some research first. “That way you’ll know a genuine bargain when you see one.”

For example, a pair of Bose Quietcomfort headphones at the retailer was £249 on Black Friday but had been cheaper or the same price on at least 15 occasions in the previous six months.

Shoppers are also being warned to watch out for Black Friday scams. Electronics, trainers, phones and clothing are all popular products used to trick people.

Criminals set up fake websites and may offer goods that are bogus, shoddy, or never arrive.