If you try to contact Indy Cube, a provider of workspaces in Wales, after 5pm you receive an automatic message that would make a good manifesto for the fast-growing four-day week movement.

“We’ll get back to you pretty quickly during working hours,” it says. “If you’re messaging us outside of these, we’re probably busy with other things, like horse-riding, karate, or good ole-fashioned sleep.”

The firm is one of a growing number of employers giving their workers an extra day off for the same pay as a five-day week. There is emerging evidence that it can boost productivity for bosses and happiness for workers. Playgrounds, garden centres and gymnasiums are filling up on Fridays with people extending their leisure into a five-day working week that has been a staple of western culture since Henry Ford adopted it in 1926.

String of British firms switch over to four-day working week Read more

And it is not just small businesses that might be spotting a chance to save a little money by turning the lights off one day a week. A marketing company in Glasgow, Pursuit Marketing, that switched 120 people to four days in late 2016 claims it has been instrumental in a 30% increase in productivity. Perpetual Guardian, a New Zealand trust business that supervises nearly NZ$200bn in assets, has switched its 240 employees to a four-day week and has reported a 20% increase in productivity. A string of small businesses in the UK have contacted the Guardian to enthuse about higher productivity, greater staff satisfaction – and even bigger profits. Talk of family lives reinvigorated and stress levels plunging abounds.

In January, the Wellcome Trust became the biggest UK employer to join the trend when it announced it was exploring switching 800 head-office staff to a three-day weekend. Labour is flirting with how the idea could fit into its policy programme: the shadow chancellor, John McDonnell, has commissioned a leading economist, Professor Robert Skidelsky, to investigate.

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And yet, for all the excitement that we may finally be moving towards John Maynard Keynes’ 1930 vision that by now we would all work a 15-hour week and spend the rest at leisure, most people who want to work less simply can’t.

Since the financial crisis, people in the UK have in fact been working longer, not shorter, hours, as stagnating wages have seen us try to take on more work to keep up with inflation. In 2011, decades of falling hours went into reverse and Britons started working longer again. If the trend for falling hours had continued, we would be enjoying the equivalent of an extra week and a half’s free time each year by now.

Automation and artificial intelligence, billed as drivers of greater leisure, have been harnessed by the barons of the gig economy to the opposite effect for some workers. Many of the 1.1 million self-employed people who access work through online platforms including Deliveroo and Uber, as well as white-collar apps such as Upwork, are squeezing in more and more tasks to keep their earnings in line with the cost of living. They face periods at work – say waiting for a taxi fare, or for parcels to be collated before delivery – with no pay at all.

“The economic fundamentals are going against the grain of the politics of hours reductions,” said Torsten Bell, director of the Resolution Foundation thinktank. “Our object should be to get them on track.”

A growing number of people are trying to do just that. Pursuit Marketing is in the hip west Glasgow area of Finnieston, and is a typical part of Britain’s service-driven economy. Pursuit’s 120 workers staff a call centre and digital marketing operation selling services on behalf of computer companies such as Google, Microsoft, Oracle and Sage. Since 2011 they have worked a regular week – 8.45am to 5pm Monday to Thursday, and a shorter day on Friday, ending at 3.30pm. But in September 2016, management wanted to increase workers’ productivity. They had noticed that workers on reduced hours, to fit in school runs or look after family dependents, were making around 17% more sales than the full-timers.

Director Lorraine Gray said: “The time off was valued, so they wanted to make sure they could keep it and they would attack their day. They were clear in their focus and there was less small talk by the water cooler.”

The firm took the decision to cut everyone’s working week to Monday to Thursday, without changing pay. She said staff responded with “a lot of noise, a lot of excitement” as the new working week took hold. In the first four weeks, sales spiked by 37%.

“People thought: if we can make this work, we can keep it,” said Gray. The increased productivity has since stabilised and turnover is up 29.5% after two years, the majority of which Gray attributes to the switch to a four-day week.

Gray said clients also appear to like the four-day week, because staff with whom they have built relations are less likely to leave (just two left in the last 12 months). Recognising that water-cooler chats are still an important part of work, the firm offers free pre-shift breakfasts so workers can spend a little time gossiping before business begins.

Facebook Twitter Pinterest Jon Freeman, a salesman with Glasgow’s Pursuit Marketing, enjoys a Friday off with his wife Clare and elder son Jon. Photograph: Katherine Anne Rose/The Observer

Jon Freeman, 33, a travelling salesman for the firm, said it has given him more energy while at work, he gets to look after his boys aged two and five every Friday, and his wife Clare is free to take on more hours in her work as a pharmacy dispenser.

“I am more focused and driven because I appreciate the extra time off,” he said. “I used to really watch the clock at the weekend because I never felt like I had long enough off, but now when I come back on Monday I really attack it.”

One of the biggest organisations to make the switch is Perpetual Guardian, whose shift has generated huge global interest, with 400 organisations from around the world asking it for advice.

“This week we have had people contact us from Japan, Canada, the UK, France, Switzerland,” said its founder and chief executive, Andrew Barnes. “The week before it was Bulgaria.”

The day off that each worker takes varies, depending on the team’s needs at the time, but there has been a change in culture with “less time surfing on social media, fewer unnecessary meetings”, said Barnes. Staff have taken to putting flags in pots on their desks as “do not disturb” signs.

“This is an idea whose time has come,” said Barnes, a four-day week evangelist who says he has spotted “a chance to change the world”. “We need to get more companies to give it a go. They will be surprised at the improvement in their company, their staff and in their wider community.”

He said it helps level the playing field between women and men, partly by making it easier for mothers returning to work because they don’t need to commit to five days, and by making men more available for domestic duties.

Research into what we might do with more time has produced some bracing results. A 2010 study by US economic psychologists investigated how 909 women would schedule a 16-hour day to maximise wellbeing. Only 36 minutes were allocated for work, compared with 106 minutes for “intimate relations”, 82 minutes for socialising and 56 minutes for shopping.

Maybe more “intimate relations” would be good for the economy. Britons work on average 1,514 hours each annually, a full four weeks more than in Germany, but are less productive. Germans and Americans produce GDP worth $60.50 and $64.10 respectively for every hour, compared with $53.50 in the UK.

Facebook Twitter Pinterest Michelle Hodge, who works at Pursuit Marketing in Glasgow, uses her day off to get a haircut. Photograph: Katherine Anne Rose/The Observer

“Productivity relies not just on the sheer amount of hours put in, but on the wellbeing, fatigue levels and overall health of the worker,” reported Autonomy, a new consultancy and thinktank examining the shorter working week, in February.

Productivity drops after the 35th hour of weekly work, according to a 2014 study for the Institute for Labour Economics. A study of call centres found that calls were handled less efficiently the longer people worked. When they work shorter hours, people tend to be more relaxed – and more productive.

But Bell, a former Treasury adviser under Labour, is one of those sceptical that productivity gains would be enjoyed across the economy. “It is very hard to assert that overall output will rise if you cut 20% of your hours across the economy as a whole,” he said. The talk-radio host Nick Ferrari put it more bluntly recently saying it was “an insane notion”.

Meanwhile, the Confederation of British Industry, which represents major employers, is unmoved by a four-day week. “At a time when flexible working is becoming more essential than ever, rigid approaches feel like a step in the wrong direction,” a spokesman said. “Businesses are clear that politicians should work with them to avoid policies that work as a soundbite but not a solution.”

Labour’s Skidelsky review is certainly finding it complicated. Rachel Kay, a researcher on the project, said working fewer hours for the same money could work in task-focused sectors where employers don’t need people available all the time, but is less likely in, for example, retail – the UK’s biggest employer – where presenteeism is required.

“A common complaint after France’s move to the 35-hour week was that companies intensified work to an unpleasant degree, making work more stressful,” she said. “So whether a shorter working week without new hires would result in improved wellbeing for employees depends on the existing workloads in any given workplace.”

“If we all shut up shop on Thursday, what do we do on the weekend?” said Kate Cooper, policy director at the Institute of Leadership and Management. “Unless, like the Swedes, we go and commune in the woods, we need other people to be working. So who is the four-day week for? I am desperately trying to see how this isn’t going to be for the privileged few. [In] anything that is customer-facing or involving a dynamic or volatile environment, you don’t have the luxury.”

John McDonnell shapes Labour case for four-day week Read more

The reasons behind increases in productivity are not yet clear. Cooper said that “the Hawthorne effect” may be in play; that is, people change their behaviour simply because they feel they are being observed – in this case they feel that by being granted a four-day week they feel their bosses are interested in their work.

“How sustainable is that?” Cooper asked. “Where does the lovely feelgood factor come from if everybody is doing it?”

And she had reservations about what might be lost by the removal of the fifth day of the working week. “What is being pushed out? What was happening on that fifth day? Were people forming strong social bonds? Were they getting a sense of the company culture? If work is just about getting a job done, a list of tasks, then the sense of purpose and social bonding that comes from employment might not be there.”

• Robert Booth is the Guardian’s social affairs correspondent

This article is part of a series on possible solutions to some of the world’s most stubborn problems. What else should we cover? Email us at theupside@theguardian.com

• Wednesday 13 March 2019, at King’s Place, London: Should we all work a four-day week? A Guardian live event with Mark Rice-Oxley