The world’s biggest trial of a four-day working week has been hailed a “major breakthrough” after most companies involved said they will keep to the shorter week following the pilot.

The findings of the pilot scheme will be presented to MPs on Tuesday as campaigners urge lawmakers to give every British worker a 32-hour working week.

The trial saw 61 companies across a variety of sectors in the UK commit to reducing their working hours for all staff by 20%, for six months from June last year.

Crucially, the firms had to make sure there was no reduction in wages for their employees.

At least 56 out of the 61 firms that took part said they plan to continue with the four-day working week, while 18 firms confirmed the policy has become a permanent change.

Just three companies said they have paused the four-day working week in their organisation for the time being.

Academics at the University of Cambridge and the US’s Boston College carried out the research, and the trial was co-ordinated by not-for-profit organisation 4 Day Week Global, in partnership with think tank Autonomy and campaign group 4 Day Week Campaign.

The results revealed a significant drop in the rates of stress and illness among the approximately 2,900 staff trying a shorter working week.

Around 39% of employees said they were less stressed compared with the start of the trial, and the number of sick days taken during the trial dropped by around two thirds.

People were much more likely to stay in their jobs, despite the trial taking place amid the “great resignation” period where workers have been quitting at record rates in search of greater flexibility, the report said.

There was a 57% drop in the number of staff leaving the participating companies compared with the same period the previous year.

At least 56 out of the 61 firms that took part said they plan to continue with the four-day working week following the pilot (Alamy/PA)

And levels of anxiety, difficulty sleeping, and burnout decreased substantially, while more staff reported that balancing care responsibilities had become easier.

The results even found that company revenue increased slightly by 1.4% on average over the trial period, and by a much higher 35% when compared to the same six-month period in 2021.

However, several staff at one large company reported concerns about increasing workloads, finding their work intensified or they were battling to work through lengthy to-do lists in the time available.

The results also revealed that some managers and staff felt the focus on efficiency had made the workplace less sociable, which was a particular concern for the creative companies involved.

But Joe Ryle, director of the 4 Day Week Campaign, said the trial is “major breakthrough moment” for the campaign towards a four-day working week.

“Across a wide variety of different sectors of the economy, these incredible results show that the four-day week with no loss of pay really works”, Mr Ryle said.

“Surely the time has now come to begin rolling it out across the country.”

Organisations across a range of industries took part. Eight firms were in the marketing and advertising sector, followed by seven in professional services such as an asset management firm in Liverpool and an insurer in London.

Five firms in the charity and non-profit sector took part, including Citizens Advice in Gateshead in Tyne and Wear.

There were also firms in the education, finance, healthcare and online retail sectors involved – and even a fish and chip shop in Norfolk.

Most firms chose to give all their staff Fridays off, while some said they could take Monday or Friday, and others opted for no common day off among staff.

Dr David Frayne, a research associate at the University of Cambridge, said: “We feel really encouraged by the results, which showed the many ways companies were turning the four-day week from a dream into realistic policy, with multiple benefits.”

The researchers insisted the results show the four-day week is “ready to take the next step from experimentation to implementation”.

“The benefits of a shorter working week for no reduction in pay are now both well-known and well-evidenced: employees are happier and healthier, and the organisations they work for are often more productive, more efficient, and retain their staff more readily”, it concluded.

The campaigners and academics will present the results at an event in the House of Commons on Tuesday.

It is being chaired by Peter Dowd, a Labour MP who brought forward the 32-Hour Working Week Bill in October, which would reduce the maximum working week from 48 hours to 32 hours for all British workers.