About five years ago, when the fashion for sweatpants seeped out of the sportswear category and dipped into the more formal zones of our wardrobe – cue grey sweats teamed with heavy black brogues, button-down white shirts and navy blazers – it seemed as if the classic trouser was heading for extinction. A bit like the onslaught of the grey squirrel, the grey sweatpant was fast becoming a more superior species, forcing its dandyish rivals to retreat to the back of the closet.

Today, it still reigns supreme. While it didn’t quite manage to become a workwear as well as a workout staple, it does appear to have become the most cherished item of a man’s wardrobe; knocking blue jeans back into second place. Saunter through the Westfield shopping centre in White City, where the MR PORTER London office is situated, and you will see little else. They are nearly all made from that dove grey cotton, worn loose, and often styled with a matching sweatshirt.

The appeal of the sweatpant is one of contrasts. As we know, it was invented in the 1920s for athletes, adopted in the 1970s and 1980s by the hip-hop community (most famously, perhaps, by Run-DMC), and from there its appeal grew and travelled across the globe. The fact that British prisons then made the grey sweatpant standard uniform for new inmates only helped further its street appeal.

And the zeal for sweatpants shows no sign of abating. They have survived an attack by the onesie; ignored the fact that the matching top-and-bottom look is also standard wear for small toddlers needing easy-access nappy changes; and smirked at nightclubs who refuse entry to those wearing a pair.

For an item of clothing to gain such wide generational appeal, for quite so long, there must be more to it than mere fashion, and a reason many high-end designers – from TOM FORD to Brunello Cucinelli – all sell luxury cashmere versions at corresponding expense, season after season.

Look around you and many sweatpant wearers are not off-duty Olympians, nor on their way home from a rap battle. They like pulling on their sweats each morning because they require little effort (no belts or zippers) and the waistband happily expands as you dig into your builder’s breakfast or lunchtime pint. You can bung them in the washing machine and not give them an iron, and they enable you to lie on the sofa, absent-mindedly fiddling with your bits, while you watch your favourite sports team run around the pitch doing all the exercise you’re dressed to do.

And it’s for this reason that the sweatpant will never successfully infiltrate the office – even the more casual, creative one. However comfortable, expensive or clean your track pants might be, they just don’t reek of industry. For an item of clothing whose origins lie in skilled athleticism, they emanate inertia. The century following their invention – despite the popularity of gym classes, yoga and athleisure – has seen the energy wringed out of them.

If you think I sound dismissive of the sweatpant, I’m actually an avid fan. If you escape to the country each weekend, as I do, they are perfect for pubs, dog walks and watching Peaky Blinders. And I did, one Friday a year or so ago, don a pair to the office. However, it didn’t feel right – despite the fact it’s quite a casual office, despite the fact it’s at the top of the aforementioned Westfield shopping centre to which everyone wears little else, despite the fact that they were one of the pairs, with white stripes, by Thom Browne, it still felt like I’d walked into the office at the weekend by mistake. When I sat down at my desk, I started automatically looking for the TV remote. My feet kept trying to perch themselves on the chair next to me, my hands reached out for a bag of nachos. It was wrong.

Perhaps a true sign that sweatpants were clearly an inappropriate choice to wear to our offices is the fact that one of my colleagues noticed it, remembered it and 18 months later asked me to write about it. An appropriate office outfit is one that nobody remembers at all.