WATCH: Sophie Raworth investigates supermarket price promotions
Britain's biggest supermarkets spend a lot of advertising money telling us they offer great value. But an investigation by Panorama has revealed that not all "bargains" are quite what they seem.
The deals at Asda, Tesco, Morrisons and Sainsbury's might seem to be everywhere, but strip away the jargon and catchy promises of "huge savings" and "special offers" and you are just as likely to find tactics that experts say range from a bit cheeky to others that could lead to prosecutions for breach of consumer protection regulations. Among them:
The 'Wow' Factor?
At Asda, the well-publicised Special Offers area of their online shopping site was offering Wow deals. They told us that it meant they were cheaper than they would normally be.
But a check of the price histories of some of the Wow items found that 11 had been for sale at the same price for at least six months - so no savings there - and four items were actually more expensive than they used to be.
Deborah Parry, a lawyer who advised the government on EU consumer protection regulations and British law, says the Wow labelling could be a breach of the law.
"Your average consumer when they learned the truth that the price was not reduced and in fact had been increased almost certainly would not purchase them."
When contacted by the BBC, Asda said the products should not have been advertised as Wow and removed them from the website.
The Multi-buy non-deal
This is the advertising on the shelves that announces Two for £2, but fails to highlight that there is no saving there - the item's price is £1 each.
But does it make us buy more?
Psychologist Gorkan Ahmetoglu, who wrote a report for the Office of Fair Trading on the influence promotions and offers of savings have on shopping habits, says this type of advertising acts as a subconscious trigger.
"They are triggering the same reaction as when you eat chocolate. The offer will still attract your attention and a lot of people will not look at the single unit price."
The new - yet old - low price
This is known as price establishing in the marketing world. A retailer sells a product at a certain price for a long period of time, but then suddenly raises it. Later, the price is dropped back to where it was in the first place and the supermarket tells us that it has "slashed the price".
Supermarkets: The Numbers
UK consumers spent £96bn in supermarkets last year
£65bn was spent in Tesco, Asda, Sainsbury's and Morrisons
The big four opened 200 new stores in the past year
Tesco's Big Price Drop seemed to do this with its medium whole fresh chickens, which rose from £4 up to £5 for a little over two months before the Big Price Drop saw it drop back down to the original price of £4.
This one is perfectly legal so long as the higher price is in place - or established - for 28 days, or is in line with consumer expectation - which is where they might run into trouble with the regulations.
Deborah Parry says this too could be a breach of the laws meant to protect the shopper.
"If it could be established that the average consumer was being misled by the suggestion of a previous higher price... then it could lead to a criminal prosecution."
Tesco says this pricing practice had breached no rules and defended the price rises before the Big Price Drop, saying it was launched in a period of significantly higher food costs and that the campaign was to help combat inflation not eliminate it.
Where are the scales?
While loose fruit and veg seems to be priced per kilo, some packaged items are often only priced per pack, with no weight listed.
At Sainsbury's, a pack of five bananas cost £1. Bought loose, the same number cost just 42p.
The packed bananas were actually almost 99p per kilo more expensive.
At Asda, it was the three red onions in a net bag that cost £2.85 a kilo, compared with just 86p a kilo if bought loose.
At Morrisons, it was the other way around - a bag of Empire apples cost £1.82 a kilo, but if you bought them loose it would be £2.99 a kilo.
All the supermarkets told us customers liked to have the option to buy by weight or by number.
John Bridgeman, the former head of the Office of Fair Trading, says supermarkets have a responsibility to be straight with their customers.
"We've got to do much better at giving people the information they need to buy carefully, properly and secure value."
Buy Now! Buy Then?
A label with a price that says Now £2 but fails to mention what the older "then" price was.
At Morrisons, fabric conditioner was labelled as Now £2 - Offer Ends Sunday but neglected to mentioned that two weeks earlier it had cost only £1.65.
For their part Morrisons said the product had been more expensive earlier in the year so the £2 still represented good value.
Less is more - much more
When "bigger pack, better value" in fact means, bigger pack, costs more.
At Asda, a 1kg tub of Clover spread was £3.20, 20p more than buying two 500g tubs of the same.
At Morrisons, the "value" pack of the same spread was £1.70 more than the two smaller packs.
At Tesco, the Vanish stain remover was £12 for the "big value" size - a full £3 more than the if you just bought three smaller containers with the exact same amount of product.
The supermarkets said manufacturers often put the value labels on their products. They say they offer thousands of deals and display unit prices so shoppers can compare items.
Panorama: The Truth About Supermarket Price Wars, BBC One, Monday, 5 December at 20:30 GMT and then available in the UK on the BBC iPlayer.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.