Companies involved in the world's biggest four-day week pilot are struggling with rota chaos and staff confusion, with bosses reporting that the policy may not survive beyond the trial.
Over 3,000 people working for 70 businesses, ranging from the Royal Society of Biology to a fish and chip shop in Norfolk, have been working a four-day week with no loss to pay since June as part of a nationwide pilot scheme that could transform working life in Britain.
While some chief executives involved said they have noticed benefits, including greater productivity and happier staff, others are starting to question whether they can realistically continue once the pilot ends in December.
"It's more likely that we won't carry on now," said Samantha Losey, who runs communications company Unity. "One of the things that has struck me is whether or not we are a mature enough business to be able to handle the four-day week.
"The rest of the world not doing four day weeks makes it challenging. We agreed we'd go all the way through the pilot, but I'm questioning whether this is the right thing for us long-term. It's been bumpy for sure."
Ms Losey said there have been difficulties on handover days as staff take different days off.
Others are also questioning whether the model can become permanent. Claire Daniels, the chief executive of Trio Media, said the shorter week has complicated hiring as she cannot promise that it will remain company policy beyond December.
"The only challenge is in recruitment currently as we cannot guarantee that we will continue the four-day week pilot scheme," she said.
Christine MacKay, the chief executive of animation studio Salamandra, said her company has not even been able to start the trial yet because they have had too many big projects on.
"I've had mixed responses [from staff] - some are very excited and some are not so keen as everyone works at different speeds," she said. "It's quite a stressful prospect if you naturally work at a slower speed. The minute the company or customers are in jeopardy it will stop."
Despite the challenges, many of those who have taken part in the scheme say staff already seem happier and more motivated. Productivity has also improved in many cases.
Matt Bolton, the creative director and co-founder at Mox London, said it has been the "best business decision" he has ever made.
Researchers involved in the pilot are analysing how employees respond to having an extra day off in terms of productivity, performance, stress and burnout, as well as job and life satisfaction.
Joe O'Connor, who runs the "4 Day Week" campaign, said feedback has been "overwhelmingly positive from companies taking part".
"In a trial with 73 companies which is after all an experiment, it would be expected that this might not work out as planned for all companies and result in a 100pc success rate," he said. "We provide ongoing support to all trial participants."