New research reveals that supermarkets are resorting to a range of tactics to stealthily increase prices without raising the suspicions of shoppers. 

As the pound remains low since the referendum there have been some inevitable price rises, but there are signs that more surreptitious methods are being used to pass on the cost to shoppers.

Here are the ones you need to watch out for on your next shop.

Occasional items

Research from comparison site MySupermarket shows shops have been pushing up the prices of less frequently purchased goods, which shoppers aren’t necessarily tracking for price differences.

It found dental floss had surged 17% in six months, while the cost of lightbulbs had jumped nearly 20% over the same period.

The prices of baby sterilising equipment (up 11%), ink cartridges (13%) and greaseproof paper (13%) have also jumped.

As we shop for these items infrequently, supermarkets are banking on the changes going unnoticed.

In contrast the price of staple products we buy regularly, like milk and pasta, have remained largely the same.

Luxury items

Shoppers that buy so-called ‘luxury items’ are also being targeted by the supermarkets.

Plants, seeds and bulbs are 26% more expensive.

Fresh trout, cashew nuts and cocktails have seen an 8% price increase, while the price of water filters has crept up 9%, according to MySupermarket data.

Own-brand items

Supermarkets are also using own-brand items to sneak in price rises we are less likely to notice.

In February, the prices of own-label food and drink (excluding promotions) shot up 1.2% compared to branded items which were down 0.5%, according to data company IRI.

It’s the first time in three years that prices for own-label products have gone up.

However, while own-label prices are rising faster than branded ones, unbranded goods remain a lot cheaper.

Fewer promotions

Supermarkets have also drastically cut back on promotions.

Data by retail analysts Assosia found that ‘buy-one-get-one-free’ (BOGOF) and ‘2 for 1’ offers fell by 29% last year.

This could be down to the backlash on multi-buy promotions last year after it was revealed that some supermarkets were not providing good value in multi-buy deals compared to buying a single item.

In August 2016, Sainsbury’s scrapped multi-buy offers altogether in favour of simpler pricing. While Tesco and Morrisons have also pledged to reduce the number of multi-buy promotions they run.

Anchoring

Another tactic supermarkets use is ‘anchoring’.

This relies on the human tendency to rely on the first bit of information they see when making decisions.

In a supermarket, this bias will mean if we see three different-sized packs of the same item priced at £10, £4 and £2, we automatically go for the £4 pack as we assume it's a better deal, even if in fact that isn't the case.

Christian Mole, executive director at consultants EY, told the Independent: “If there are three options at say £2, £4 and £10, consumers will generally pick the £4 option.

"The £10 option is there to “anchor” a shopper’s initial price impression, and induce them to buy the slightly more expensive (and higher margin) option.” 

Shrinkflation

In February, Channel 4’s Dispatches programme revealed how manufacturers and supermarkets were cutting the size of products but not the price.

This practice of ‘shrinkflation’ means you get less for the same amount, or more money, and has hit the headlines when it's happened to the likes of Tolberone, Doritos, Mars chocolate and Peperami.

But the Dispatches – Supermarkets: Brexit & Your Shrinking Shop programme shows it’s not just a phenomenon impacting chocolates and snacks.

The show used research from MySupermarket to identify shrinkflation on things a range of everyday groceries.

For example, at Tesco, packets of curled parsley were found to have shrunk from 35g to 30g but still cost 70p – which is effectively a 17% price rise.

At Asda, its Butcher’s Selection turkey mini fillets were found to have shrunk from 573g for £3.50 to 500g for £4.50, which amounts to a price rise of 47.3%.

[Read more: Groceries 'shrinking while prices stay the same']

What’s next for supermarket prices?

Supermarkets are running out of options.

Years of price wars have left little room for manoeuvre on price margins and the fall in the value of the pound will continue to make it tough for supermarkets to keep the price of staple goods the same.