Which? reveals the groceries that cost three times more depending on when you shop

The prices of popular groceries can vary by up to 284%, Which?'s biggest ever pricing investigation has revealed.

Our statisticians have crunched over a million prices to uncover just how much, and how often, the price of branded products in our supermarkets change. 

They have exposed some eye-opening pricing secrets - from the supermarket where you’ll pay almost four times the amount for the same product on some days than others, to the grocer that almost always beats its rivals when it comes to the cost of branded groceries.

The groceries with the most dramatic price changes

We looked at the prices of 493 branded grocery products at Asda, Morrisons, Ocado, Sainsbury’s, Tesco and Waitrose every day throughout 2020.

Lavazza Qualita Rossa Ground Coffee (250g) at Ocado had the dubious honour of being the product with the most dramatic price difference in our investigation. Bought on a good day in 2020 (of which there were 63), it would have cost you £1.30. But if you unknowingly picked one of the 130 bad days, you would have been stung for a whopping £5.

That’s 284% more for exactly the same product.

Ocado told us the fluctuation in price was 'a technical error' which had now been fixed.

But it’s not just coffee that could leave a bitter taste in your mouth. Other products you should never pay full price for include Muller Light Greek Luscious Lemon (4x120g) and Walkers Sensations Crisps Thai Sweet Chilli (150g), which varied by 175% and 167% respectively at Sainsbury’s.

And watch out for Carte D’or Vanilla ice cream (1L) at Asda, which fluctuated by 133%.

• Find out more: which is the UK's cheapest supermarket?

Supermarket price wars

Overall, we found the prices of almost all the products in our investigation varied regularly on a high-low basis at all six supermarkets. Most of the products could be found on discount at one or more retailers at any one time.

Take the Muller Light Greek Luscious Lemon (4x120g). Its biggest variation in price was 175% at Sainsbury’s, where it alternated regularly between £1 and £2.75 at roughly three-week intervals.

The cheapest price we found for it was 95p at Asda, and £1 at most of the other supermarkets. In fact you could find it for £1 or less in at least one of the major supermarkets for about 85% of the year.

The changing price of a Muller yogurt

Every supermarket employs expert teams to monitor competitors’ pricing using sophisticated software. Prices are adjusted accordingly – sometimes to undercut, and other times to match or track slightly above or below. 

• Find out more: best and worst supermarkets

Where to head for the best bargains

For this investigation, we looked at 19 popular categories of branded groceries, from chocolate to cheese. Asda offered the cheapest average prices for all of the categories we looked at, making it a good bet if you like branded food and drink but don’t want to pay over the odds. 

Meanwhile, Waitrose was priciest for eight categories and Ocado for seven, so don’t head to these upmarket rivals if you like to be spoiled for choice with branded bargains.

Sweet-toothed shoppers should be particularly mindful of prices, with cakes and cookies fluctuating by 48% – more than any other category we looked at. This was followed by juice drinks and smoothies (41%), cooking sauces (38%), crisps (36%) and cereal (35%). Wrapped bakery item prices moved around the least on average, although they still changed by 13%.

• Find out more: how to spend less at the supermarket

Are promotions a bad thing?

Price promotions are so well established in UK supermarkets that they have become deeply entrenched in many people’s weekly shop.

When we surveyed shoppers in March*, 43% told us they always or often buy groceries that are on offer as part of their main shop. And straightforward price reductions are the most common type of promotion opted for, with half of UK adults saying they bought a discounted product last time they went food shopping.

When you genuinely save money on something you were actually planning to buy, that’s good news. But when products are regularly discounted, it calls into question whether the higher price is artificially inflated to account for planned, regular discounting – not such good news for shoppers, particularly those who are distracted, in a rush or unaware the item is likely to be cheaper next time they visit.

One in five of our survey respondents said they found grocery promotions confusing. And when you factor in not just discounts but multibuys, special loyalty scheme prices, meal deals and buy-one-get-one-free offers, there’s certainly a lot to consider when trying to get the best price.

• Find out more: supermarket loyalty cards compared

What about Aldi and Lidl?

In the world of grocery pricing, Aldi and Lidl are undoubtedly the retailers to beat – but we couldn’t include them in our investigation as we focused exclusively on branded items, which the discounters stock fewer of. 

Aldi and Lidl focus on everyday low pricing. Shoppers don’t need to read smallprint, squint at prices per gram or carry a calculator to get the best deal.

So how do Aldi and Lidl keep their prices so low? Firstly, they stock far fewer lines. This results in economies of scale, which push prices down.

Chris Elliott, head of market insights at data analyst Edge by Ascential, told us that the other major supermarkets are also beginning to do this in order to compete.

While product quality doesn’t suffer too badly in return for low prices – both Aldi and Lidl scored three stars on this measure in our latest supermarkets survey – shoppers don’t love the lack of range, awarding both discounters just two stars for this. The no-frills store format, another way in which costs are kept low, also scored Aldi and Lidl just two stars.

Clearly, there’s still hope for the mainstream grocers, and some are openly competing: Sainsbury’s and Tesco have both launched Aldi price-matching schemes, which they hope will win them back customers in an increasingly price-conscious market.

Tips to help you save

If you don't want to pay over the odds for your supermarket shop, here are some tips:

1. Don’t pay full price: If you regularly buy non-perishable branded groceries like crisps, cereal and tins of soup, make sure you stock up when they’re discounted (if you have the storage space at home), and avoid paying full price wherever possible.
2. Shop around: The rise of online shopping means you don’t have to feel tied to your nearest big supermarket. And while they don’t offer online grocery shopping, Aldi, Lidl, Home Bargains, Wilko and others often offer good deals on branded products too. It’s also worth trying own-label alternatives, which can offer great quality at even better prices.
3. Watch out for pricing tricks: Discounts are great, but don’t be manipulated by other pricing tricks. The strawberries may be on offer but what about the price of the upmarket pouring cream temptingly (and deliberately) positioned next to them?
4. Scrutinise price-matching claims: Sainsbury’s and Tesco both shout about their Aldi price-matching schemes, but they actually only cover a limited range of products. Once you’ve filled your trolley with everything on your list, you may find your overall shopping bill is still more expensive.
5. Take advantage of loyalty scheme discounts: Lidl Plus and Tesco Clubcard are just two examples of supermarket loyalty schemes offering exclusive discounts to members. You can get some good deals this way so it’s worth signing up with all the stores you use if you’re after a bargain.

Find out more: loyalty schemes compared

*Results based on an online survey of 2,000 members of the public conducted in March 2021. Data has been weighted to be representative of the UK population (aged 18+).