Michaela Reaney thought introducing a four-day week to her business would be a "no-brainer". She imagined that her 35-person team would be thrilled to get an extra day off, with no reduction in pay or expectation to work extra hours.

But two months into the trial and it was clear that it wasn't working as intended.

"There were a few people who experienced serious levels of stress from cramming so much work into the four days to be able to allow themselves to have an extra day a week off," says Reaney, who runs Yorkshire-based training firm Opportunity Global. "It added an extra layer of pressure people didn't feel comfortable with.

"It was also challenging for our working parents, who felt guilty for doing the school run. People were finding that by ring-fencing this day a week, they felt incredibly uncomfortable about taking flexibility at other points in the week. It was never our intention to put more stress or more pressure on people, but we did."

More than a dozen MPs have called on ministers to transition away from a five-day working week, following the 200 companies that have already made the switch permanently. But the less publicised consequences of a four-day week shouldn't be ignored.

Behind the positive headlines relaying the benefits of working less for the same money are statistics pointing to some dark side-effects. According to results of a 2022 UK pilot involving 61 companies and 2,900 workers, 22pc reported higher levels of burnout than when they had been working five days. Some 13pc said they were more stressed, and 16pc noted a decline in their mental health.

Reaney found that 40pc of her team struggled with a four-day week. She came to the conclusion that she couldn't responsibly continue with it, and shut the trial down a month early. That was in 2021, and now she believes her employees are better off in an environment that offers more flexibility over five days. For example, there are team members that like to do mid-morning gym sessions, and others who prefer to start and finish their day later.

"What we have now is, in some respects, harder to manage, as everyone has very personalised flexibility," says Reaney. "But the level of productivity and wellbeing is so much higher because people have that control and that personal experience in the workplace."

After spending a year working in a company with a four-day week structure, Karim Adib says he's happier working five days a week in his current role - despite his friends calling him crazy for voluntarily giving up an extra day off a week.