For many, dressing for an extreme heatwave means wearing as little as possible. But for some men, not even record-breaking temperatures can dissuade them from pulling on their favourite pair of jeans.

This week as temperatures in the UK rose sharply on the back of the climate crisis, Andy Burnham stuck to his tried and tested “cool dad” combination of dark jeans with a dark blue (not black as he pointed out to Kemi Badenoch) T-shirt as he made his way to London to be sworn in as MP for Makerfield.

Despite brands at Paris men’s fashion week handing out umbrellas and iced towels to guests in an attempt to keep them cool, the front rows have been peppered with attendees wearing jeans. Meanwhile, although Dior moved its show from an afternoon slot to early morning to avoid the heat, the label’s designer, Jonathan Anderson, still wore his uniform of vintage Levi’s jeans and Salomon trainers as he took his post-show bow on France’s hottest day on record.

It isn’t just the fashion crowd holding fast to denim: John Lewis reported sales of Burnham-esque indigo jeans from Nudie were up 3% this week, searches for Carhartt jeans were up 100% week on week while straight fit Edwin jeans were up 200% compared to last week when temperatures were at a much cooler level.

“Men in shorts is the reason why men are wearing jeans,” says Henrik Lischke, the fashion news and features director at Grazia. “Shorts have become such a sticky topic fashion-wise that a lot of men haven’t quite figured them out. Jeans with a T-shirt or shirt is just an easier way to crack summer dressing.”

For Andrew Groves, a professor of menswear systems at Westminster University, the trend can be read as a comment on masculinity. “Wearing jeans in a heatwave is not really about comfort,” he says. “It is about how menswear trains men to dress within systems of utility, restraint and masculine control, even when those systems stop making practical sense.”

However, many jeans wearers argue that as they are made from cotton they are naturally breathable so don’t cause them to overheat. This is one of the reasons Zak Maoui, the style director at UK Esquire, has been wearing a pair of Levi’s 501s at Paris fashion week regardless of a heatwave gripping the city. “Wearing jeans also means your legs are covered, which stops them getting burned,” he says. On the high street, jeans with an untucked shirt to allow more ventilation, or an undone shirt over a T-shirt is a popular look.

For casual occasions, Lischke prefers a 90s light-blue jean but for an office environment suggests dark indigo denim. “You definitely want to avoid stonewash or anything distressed,” he says. Footwear is also key. “A loafer with a jean is appropriate for most places,” Lischke says, but for weekends he suggests a smart leather sandal or flipflop. When Burnham isn’t wearing Adidas trainers he likes to style his jeans with Birkenstocks.

So does this new jean devotion signal a backlash to fashion’s short shorts obsession? “Shorts can be incredibly chic at any age but maybe they are best kept for the garden or beach,” Lischke says. “Everyone loves to see Harry Styles in a pair of short shorts. But there is a time and place for them.”