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19 Dec 2020

Revealed: the popular groceries you should never pay full price for

Plus the supermarkets consistently charging extra for loo roll, tea bags and more
Range of groceries

If you tend to load your favourite food and cleaning products into the trolley each week without noticing their prices, you might be paying well over the odds.

Exclusive Which? research has revealed the popular groceries and household items you should never pay full price for - and just how much the cost of your favourite brands can vary depending on which supermarket you use.

From Persil laundry detergent and PG Tips to Andrex loo roll and Kenco coffee, we reveal the cheapest and most expensive supermarkets for some of the UK's most popular trolley staples.

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Where can you get the cheapest branded groceries?

We analysed thousands of grocery prices between March and August 2020 to find the ones with the biggest price differences between supermarkets.

Persil non-biological washing liquid had the biggest price difference of any branded product in our investigation.

Persil non-bio bottle

It was, on average, £2.98 more at Morrisons than at Lidl across the six months of our investigation. Andrex Supreme Quilts toilet tissue, meanwhile, was on average £2.60 more at Waitrose than at Morrisons.

ProductSupermarket with the highest average priceSupermarket with the lowest average priceBiggest average difference
Persil Non Biological Washing Liquid (1.33l)MorrisonsLidl£2.98
Andrex Supreme Quilts Toilet Tissue (16 rolls)WaitroseMorrisons£2.60
Kenco Millicano Coffee (100g)Waitrose and OcadoAldi£2.06
Hellmanns Real Squeezy Mayonnaise (705-750ml)WaitroseSainsbury's£1.87
PG Tips Pyramid Tea Bags (240 bags)WaitroseAsda£1.87

And if Kenco Millicano Coffee, Hellmanns Real Squeezy Mayonnaise or PG Tips Pyramid Tea Bags are regulars on your shopping list, it's worth avoiding Waitrose, which was most expensive on average for all of these (jointly with Ocado for the coffee).Cheapest were Aldi, Sainsbury's and Asda, respectively.

The brands you should never pay full price for

We found some groceries fluctuated wildly in price at the same supermarket across the six months of our investigation.

Persil non-bio had the biggest average price range of any product we looked at. Its price varied the most at Morrisons, where it alternated between £5 and £10 fairly regularly - meaning you should avoid buying it when it's £10.

The product's price also varied at other supermarkets - by as much as £4 at Tesco, £3.50 at Asda and £3 at Ocado.

The fluctuating price of Persil non-bio

graph showing price of Persil at different superma

We know a popular supermarket pricing tactic is to drop a price on a popular item and advertise it as a discount before raising it again for a few weeks, only to drop it again.

This 'high-low' alternating pricing model gives the illusion of discounts, but the reality is that shoppers buying at the higher price are paying more than they should to compensate for the times when the price is lower.

Other products that fluctuated significantly in price included:

  • PG Tips Pyramid tea bags (240 bags) - varied by £2.77 at Ocado
  • Twinings English Breakfast tea (100 bags) and Twinings Every Day Tea Bags (100 bags) - both varied by £2.65 at Sainsbury's
  • Andrex Supreme toilet tissue (16 rolls) - varied by £2.65 at Waitrose

Find out more: should you trust supermarket special offers?

The own-brand groceries with big price differences

We also looked at how much prices varied between different supermarkets' own-label items:

ProductSupermarket with the highest average priceSupermarket with the lowest average priceBiggest average difference
Cooked and peeled cold water prawns (150g-200g)Ocado (Waitrose own label) and WaitroseAldi£3.28
Fresh salmon fillets (220g-340g)WaitroseAldi£2.26
Olive oil (1 litre)Ocado (Waitrose own label) and WaitroseAldi£1.81
Beef sirloin steak (173-275g)Ocado (Waitrose own label)Aldi and Lidl£1.72
Chicken korma and pilau rice (400g-500g)Ocado (Waitrose own label)Aldi and Lidl£1.51

Note: where the size of pack was given as a range, we based our results on the price per gram or ml.

Own-label prawns had the biggest price difference of any product in our investigation. A similar sized pack was, on average, £3.28 more expensive at Ocado and Waitrose than an equivalent pack of prawns at Aldi.

Of course, it's harder to draw exact comparisons between own-label products than branded items. While we used experts to ensure that the products are as comparable as possible based on a range of factors including weight, quality and other industry data, they will inevitably differ in terms of quality, freshness, and taste across different supermarkets.

Is price more important than quality?

Groceries are one of the biggest household expenses. In fact, according to the Office for National Statistics, we spend an average of £61.90 per week on food and non-alcoholic drinks - that's 10% of our household spend.

The economic uncertainty brought by COVID-19 has led to a renewed focus on price. Indeed, supermarkets are currently waging price wars in various different ways, both by trying to cut basic everyday prices and also through a range of promotions, loyalty-related discounts and price-matching.

For our investigation, we analysed thousands of grocery prices at eight major UK supermarkets - Aldi, Asda, Lidl, Morrisons, Sainsbury's, Tesco, Waitrose and Ocado - between March and August 2020.

Based on a trolley of 87 grocery items, Waitrose was the most expensive supermarket at £129.47. Discounter Aldi was the cheapest at £80.81 for the same items. That's a massive £48.66 saving - which works out at more than half the total Aldi bill.

This echoes the last few results of our monthly cheapest supermarket price check, with Aldi consistently cheapest and Waitrose priciest.

But of course, pricing is only one factor to consider when choosing a supermarket: quality, range, delivery slot availability and the in-store experience are also key.

To find out the best grocer on each of these measures, check out our guide to the best and worst supermarkets.