Bed-lam: as PJ bottoms become increasingly visible outdoors, does societal breakdown necessarily follow? / iStock

Nightwear is inappropriate dress for parents visiting a school, a headteacher has declared

If ever an issue was designed to drive a wedge between the Great British public (washed and unwashed), this is it. Parents are rebelling and staff don't know which way to look, but a certain headteacher in Darlington is standing her ground. "Get dressed for school," she says, and she's not talking to her pupils.

After noticing a growing number of adults wearing pyjamas – not just to the school gates in the morning, but also at meetings, assemblies and even the Christmas show and parents' evenings – primary school head Kate Chisholm wrote to parents asking them to wash and get dressed before the school drop-off.

"It just got to the point when I thought, 'enough's enough,'" she told the BBC. "I'm not trying to tell people what to do with their lives, but I just think being a good role model first thing in the morning – getting yourself up, getting yourself dressed, ready for business, out to school – is a really good example to set."

I work from home, but with no children to ferry to school I am thankfully spared the judgements of Ms Chisolm and her ilk. I am, however, well acquainted with the perils and the pitfalls of not-quite-getting-dressed, also known as the home-office wardrobe. I certainly aim to get dressed every morning before reaching my desk, preferring to feel clean, switched on and ready to face the day head on.

But if you ring my doorbell before midday, you might struggle to differentiate between my workwear and someone else's nightwear. With the trend for onesies, loungewear and luxe sportswear peaking this month (John Lewis has announced its "loungewear" sales are up 29 per cent year on year), it seems to have become acceptable for us to brave public spaces clad only in fleece, cotton or fluffy sweatpants, all crudely pulled together with drawstring.

Just last week, Nigella Lawson admitted to The Lady magazine that she liked nothing better than an all-day pyjama party. "If I'm not working, and especially because I work at home, I don't really see the point in getting dressed," she said. She even said she loved staying in her pyjamas when people came over for dinner. Prime Minister David Cameron has also admitted to slouching around in his PJs if he's working from home of a morning. Is this an effective way to Get Britain Working, Dave?

Psychotherapist Hilda Burke isn't so sure. "It probably depends on the type of work that you do but, as in a school, there are certain standards and codes that authority figures rely on in the workplace," she says. "It's possible they fear that if people don't dress properly for the office, standards might slip.

"The legal profession is one of the last that goes for very formal attire, and there could be a psychological link between what you're wearing and upholding the rigours of the law.

"In more creative organisations, it might be beneficial to wear what you like," adds Burke. As we know, tech giants are famed for their play-at-work approach to the office, where casual dress and larking about are encouraged.

In 2010, Tesco asked shoppers not to wear nightwear when visiting its supermarkets, "to avoid causing offence or embarrassment to others." Today, its staff might struggle to differentiate between genuine daytime attire and a slumber outfit.

Along with the comfy nightwear-as-daywear trend, a rather more glam look has emerged – that of smart silk and print pyjamas, and velvet slippers. From the catwalks of Paris to the aisles of M&S, the pages of Vogue to the This Morning sofa, the rise of the posh pyjama has further embedded sleepwear into our routines.

Sarah Knight, author of The Life-Changing Magic of Not Giving a F**k, found that a great release came with the bravado to wear her PJs to her local shop. After 15 years in a high-achieving, high-octane publishing career, she realised that she spent all her time pleasing everyone else over herself, and decided to stop caring so much. One of the things she stopped caring so much about was getting dressed and putting on make-up for visits to the cornershop, a victory she celebrates regularly by using the extra time to enjoy the gossip magazines she picks up there.

Knight probably isn't the sort of role model Chisholm wants for her pupils, but she is proof, along with Nigella, that success and respectability don't always come dressed up in a starched shirt and shiny shoes.