How can you switch off if you go to work in the same clothes you wear to bed?

Sales of loungewear are up by 29 per cent, according to John Lewis

Ariana Grande sporting a onesie in Tokyo (Rex Features)

This morning, I should be at my desk in pyjamas. I intended to write this column in my pyjamas. They are very funky, and to herald the 2016 trend for sporting nightwear across the day, I ought to have been wearing them. But I just couldn’t. As ever, I am sitting at my desk properly dressed. Right down to shoes. I know this is out of kilter, but I can’t help it. In the same way that I will never use the word “bare” to mean “large or important” (as in “these shoes are bare nice”), or write “peak” for affronted, when what I mean is “pique”, I will never start my working day, or indeed any day, in nightwear. Unless I am ill.

Yet if being on trend is where you are, then by 2 January you ought to be lolling around, if not in pyjamas, then at least in a bit of cashmere loungewear. According to that reliable bellwether John Lewis, sales of loungewear (in other words, trousers with drawstring waists, slippers and sweatshirts), was up by 29 per cent on this time last year. Simply Be, a store which specialises in plus-size clothes for women, has posted a 63 per cent rise in pyjama sales.

A spokesperson from Simply Be suggested this was because celebrities have started posting selfies of themselves in pyjamas. As with them, so with us. Seeing a shot of (say) Miley Cyrus in her jim-jams has opened the brushed cotton floodgates for us civilians. Really? If that were the case, surely we would have also all been clinging to wrecking balls, à la Miley, or at least leaping around in bikinis. And that hasn’t happened, at least not in Islington.

I think the daytime shift into nightwear has nothing to do with our herding instinct around the glossy pages of OK!, It simply reflects the fundamental alteration, even abandonment, of formal working boundaries over the past decade. For many people, the line between paid working time, and time off has almost totally vanished, thanks to the digital revolution, which has turned our bedrooms into offices and our phones into high-speed computers capable of digitally processing data, film, television and audio. The formal division between work and play is as outdated as a pinstriped suit and bowler hat, to be divested when its owner was “off”. Nobody is “off” nowadays (even though, irritatingly, six hours of sleep in every 24 is still obligatory). The duvet and dressing gown are still necessary, but they are no longer reliable indicators of anything.

This is of course brilliant news for clothing manufacturers; no longer are nighties a sort of £20-staple destined never to be seen in anything other but a crepuscular gloom. They are now a proper fashion line and are treated as such by the fashion industry. Indeed, according to yesterday’s spread in The Independent, we ought to be upgrading our “comfort wear” by investing in wrist warmers, chunky slippers, £139 silk pyjama sets from the White Company or a £195 cosy coat from a marvellous shop called (what else?), Yawn.

The blurring of boundaries is a godsend to working parents. Gone is the time when you had to extend expensive childcare arrangements in order to hover around an empty office waiting for that important phone call at 7pm; You just have to train your kids to be quiet via a previously agreed sign (rolling eyes, hissing, waving hands), when the boss calls. I have dealt with work issues while combing nits out of the heads of my children, cooking, walking the dog and the rest, as will thousands of other parents (although I did draw the line at taking a call from the Today programme once, when I was actually in labour).

Is there any downside to all of this? If you are rigorous about going offline when you want a break, then probably not. But be careful about the merging of sartorial lifestyles.

If (like me) you feel that nightwear is not the way forward, you could always take a fun run into the amazing world of gym gear, where Stella McCartney, Lululemon and Sweaty Betty will welcome you with open Lycra arms. At least such garments have a practical use: they certainly make running for the bus a bit more efficient than it might be in a skirt and heels. For those who insist on nightwear, I offer one critical caveat: wear a furry onesie during the day if you must; but although your body is in loungewear, if you are working then your mind must always be in a sharp suit. Always. Simon Danczuk, please take note.