Sunday trading laws were relaxed for the first time last weekend, ready for the Olympics, but long-awaited sunshine looks to have had more impact on sales than extended hours.

Shops across England and Wales were allowed to open for more than six hours on Sunday, following the government’s decision earlier this year to allow stores over 3,000 sq ft to trade for longer on the eight Sundays during the Olympics and Paralympic Games.

Although supermarkets typically chose to open for around 10 hours - including Tesco and Asda, which extended hours at every store - observers argued the first sunny weather across the country in three months boosted sales more.

The ACS, which vehemently opposed the temporary relaxation of the trading laws and argued it would cost independents £480m, said the weather had made it harder to judge the impact on small shops. “We’re not rushing to any conclusions - it’s a case of wait and see,” said Shane Brennan, ACS public affairs director.

The multiples all reported brisk trade in barbecue products. Sainsbury’s, which has extended trading at just 30 of its stores, plus a further nine for this Sunday along the Olympic cycling road race route, said barbecue sales were 274% up on the week before. Other big sellers were suncare (up 250%), burgers (150%), coleslaw (100%) and salad (50%).

“As the weather has been so varied, it comes as no surprise that Brits are taking advantage of the heatwave,” said Sainsbury’s weather expert David Bailey.

Waitrose, which has extended the opening of all its stores by two hours on Sundays, said its total sales were up 8.7% last week on the year before. Sales of barbecue meats rose by 47%, free range sausages by 35% and beefburgers by 37%.

However, observers expressed disbelief that stores had failed to shout about the longer hours.

“I am staggered by the lack of exposure and publicity on this,” said Debbie Robinson, Spar MD and The Grocer guest editor. “It has been conspicuous by its absence.”

One industry expert added: “Perhaps they don’t want to attract criticism because they have kept a low profile throughout this. I would also have expected more from the garden centres and DIY chains.”

However, Tesco insisted it had clearly advertised the changes in stores and on its website.