Bargain hunters should beware that Black Friday deals don't always represent the best possible value, after a study found only around half of Black Friday deals are actually cheapest during the annual shopping bonanza.

An investigation by Which? looked at 178 deals on 20 popular tech gadgets and home appliances, and tracked the prices every day for three months before and two months after last year's Black Friday. The research found just 90 (or 51%) of the deals advertised by Amazon, AO, Argos, Currys and John Lewis were cheapest on Black Friday itself.

The remaining 88 deals were cheaper at some point in the months before or after Black Friday in 2015.

This year Black Friday falls on 25 November – to keep on top of the best deals, plus see's analysis of which are genuine bargains, check out our deals for Black Friday page.

What did the Which? research find?

Fewer than one in ten (8%) discounts were one-day only offers, where the Black Friday price was cheaper than on any other day. Around one in ten (12%) were cheaper at some point in the three months leading up to Black Friday and four in 10 (38%) were cheaper in the weeks after Black Friday.

The Which? researchers also claimed that AO and Currys appeared to inflate the 'was' price to make deals look better than they actually were.

When promoting a discount, such as 'was £100, now £50', the 'was' price should be the most recent price the item was sold at for 28 consecutive days or more, and not a price that is more than six months old. But Which? found examples where companies seen to have flouted this rule.

Indeed, it was suggested by Which? that AO and Currys may be breaking Government guidelines, though both retailers claim they followed regulations and guidelines with regard to displaying discounts.

Black Friday 'deals' which didn't live up to the hype

The following were among the examples singled out by Which?.

  • Currys sold a Samsung TV (the UE40JU6740 model) for a pound less on Black Friday 2015 – it had been £749 since 30 October before it was cut to £748 on 24 November. But for 18 days in late August and early September you could have bought it for £699.
  • AO sold another Samsung TV (the UE40J5100 model) for £299 on Black Friday, with a 'was' price of £499. Yet it was often available for £289 during November and late October. For the rest of the three months leading up to Black Friday it was £299, £309 or very occasionally £319.
  • AO sold a Samsung fridge-freezer (the Samsung RB Combi Range RB38J7255SR) for £749 on Black Friday (and claimed it 'was £999'). But it had been sold at £849 for almost every day in the three months leading up to Black Friday, so the actual discount was £100 rather than £250.
  • Currys sold an LG TV (the LG 43UF680V TV) for £449 (and claimed it 'was £899') on Black Friday. But it had not been sold at that price since August. The TV was going for a much more modest £499 from late August until early October, so this should have been the 'was' price instead.
Black Friday deals often cheaper at other times – compare prices before you buy
This year Black Friday falls on 25 November - remember not to spend what you can't afford or don't need

What the shops say

Here's how the big stores responded to Which?'s investigation:

  • Amazon said: "Six of the eight products that Which? reviewed on last year had our lowest price on Black Friday and, in response to customer feedback, we spread out great deals over several days. This year, our Black Friday sale runs for 12 days from 14 to 25 November."
  • AO said: "The internet is the most transparent market place ever created for consumers to be able to compare price and service associated with it and we work hard to be exceptional on both fronts."
  • Argos said: "We offer customers thousands of great deals over the Black Friday period and work hard to ensure that all of our offers are fully compliant with the full range of regulations and guidance in pricing practice. We certainly do not intend to mislead in anyway. We update our pricing frequently to ensure that we can offer our customers the best deals."
  • Currys disputed the Which? findings, saying: "We are proud to offer our customers fantastic deals all year round, with prices that are truly transparent and backed by our price promise.
    "We fundamentally disagree with the approach taken by Which? in this report and comply fully with the government's Pricing Practices Guidance, displaying a clear date from when the 'was' price was taken, allowing customers to make a fully informed decision."
  • A John Lewis spokeswoman attributed its prices to its 'Never Knowingly Undersold' promise, and said: "Our never knowingly undersold commitment means that we will match our competitors' deals and offers for as long as they run."
    "The sheer scale of Black Friday's great offers means that these are planned up to 12 months in advance to maximise the value and service for our customers. That demands significant planning for a very fluid trading environment across hundreds of offers and we are always focused on offering the best price match promise all year and especially around Black Friday."

How to avoid being caught out

Regardless of whether you're shopping online or braving the crowded stores, it's important to remember that Black Friday can be addictive – so don't get caught up in the hype or spend what you can't afford or don't need.

Just because it's on offer, NEVER assume it's the cheapest, and ALWAYS compare prices to ensure what you're getting is really a bargain.

For more help, tricks and tips, see our Cheap Online Shopping and 15 Shopping Secrets guides.

Additional reporting by the Press Association.