From the Easter eggs towers by the entrance to the ad hoc bins filled with Lindt Gold Bunnies and Creme Eggs near the checkout, it takes serious willpower to resist buying chocolate in the supermarket at this time of year.

This potent cocktail of prime retail space, extra displays and deals will spur Britons to spend some £370m on calorie-laden treats for the long weekend. But this Easter will be a last supper for supermarkets and their suppliers ahead of a clampdown on how foods that are high in fat, salt or sugar (HFSS) are sold in England.

In the autumn new laws, part of the government’s anti-obesity strategy, will prohibit thousands of unhealthy products, including chocolate bars, biscuits and crisps being sold from these lucrative pitches.

Volume deals such as “buy one get one free” or “3 for 2” on HFSS products will also be banned in what the retail analyst Bryan Roberts describes as the “most significant change to supermarket operations and economics since they were invented”.

“There is a reason snacks and confectionery are called impulse foods,” says Roberts. “They are not often on someone’s shopping list but people have got into the habit of picking them up. They rely on visibility for a lot of their sales and that is being taken away. This has big financial implications for retailers and suppliers.”

But the government is staring at one of the worst obesity rates in Europe, with two in three UK adults officially overweight or obese in an escalating crisis that costs the NHS £6bn a year and wider society £27bn. The pandemic has also recorded worsening childhood obesity levels in England.

In its guidance for retailers, published this month, the government says the promotional environment in supermarkets was part of the problem. It “did not always align with its healthy eating guidelines” and “makes it harder for families to make healthier choices when shopping”.

Voluntary programmes by retailers had been “very limited and unsuccessful” at changing the shopping environment, it says. A government ban on junk food advertising online and before 9pm on TV is due to kick in next year.

At a time when the soaring cost of living is weighing on households, these volume discounts might appear to be a way to save money but the evidence stacks up against them. They encourage people to buy, and eat more than they intend.

Figures from the data firm IRI give an indication of how susceptible shoppers are to these tricks of the retail trade. It estimates the sweeping changes could see sales of HFSS foods – a long list that will capture products including crisps, sweets, chocolate, cakes, crisps, biscuits, pizza and ice-cream – drop by £1.7bn a year. Analysts say that half of all chocolate is sold on promotion.

HFSS refers to foods that score four points or more, and drinks that score one or more, on a nutrient scorecard developed by the Food Standards Agency. Points are awarded for the energy, saturated fat, sugar and sodium per 100g, and deducted for things like fibre and protein.

This means not all products in a category will be affected, with manufacturers able to reformulate products to avoid being penalised – something that happened at speed ahead of the sugar tax in 2018.

So what does this shake up mean for the weekly shop? A glimpse of the future can be seen in trials being run byTesco and Sainsbury’s.

In the Tesco Extra store in Royston in Hertfordshire, , instead of chocolate, shoppers are greeted with a garden compost promotion and “clubcard price” deals on big whisky and gin (alcohol is not affected by the new rules). Shoppers must go on an Easter egg hunt if they want to buy one.

At the all-important aisle ends, the usual selection of chocolate, crisps and soft drinks has been replaced with deals on tea, coffee, tinned fruit and veg, and meal seasoning kits – not to mention calorie-free options such as toilet roll and detergent.

Shoppers are also given healthy eating cues as they shop. In the breakfast cereal aisle a sign highlights “low sugar” options such as Weetabix. Elsewhere they are told that tinned beans and veg are a “source of protein”. There is even hope for crisps fans in a section labelled “under 100 calories”.

Tesco aims to increase its sales of healthy products, as a proportion of total sales, from 58% today to 65% by 2025. When reporting a doubling of pre-tax profits to more than £2bn this week its chief executive, Ken Murphy, said it was in “good shape” ahead of the new legislation. “We’re really clear on how we’re going to re-merchandise our stores,” he said, adding that it would work with suppliers to reformulate products and make them healthier.

The looming changes have opposition from within the food industry at a time when many companies are grappling with soaring costs. Karen Betts, the chief executive of the Food and Drink Federation, said it was concerned that in implementing these measures now the government is “only adding to food price inflation”.

The rules apply to retailers with more than 50 employees and stores bigger than 2,000 sq ft (186 sq m). Promotions such as “50% off” or “save £1” are still allowed, leaving businesses with some wriggle room.

Ignacio Vazquez, a senior manager of healthy markets at ShareAction, which has campaigned to get listed companies, including Tesco and Unilever, to sell healthier food, said the impact of the new rules would depend on whether companies followed the “spirit” as opposed to letter of the law.

“Companies make decisions that have an impact on the products we buy and influence our choices,” he said. “This legislation is trying to encourage companies to do things differently so consumers are nudged to buy healthier products rather than spend more money on unhealthy food.”