The world’s biggest trial of a four-day working week has been hailed a success – with most of the companies involved saying they would continue offering a shorter week.

A total of 61 companies across several sectors in the UK were involved in the pilot, which ran for six months from June last year.

Employers had to make sure there was no reduction in wages for staff who took part in trialling a 32-hour week.

At least 56 out of the 61 firms which took part said they plan to continue with the four-day working week, including The Royal Society Of Biology based in London.

Chief Executive Mark Downs said productivity had increased.

He added: “There’s been a decline in the number of sick days taken during the period of the trial.

“Before the trial, on average, each person would take four or five sick days per year – that’s down to less than two.

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“I think it’s a substantial difference.”

Other firms involved in the pilot have had similar experiences.

Research carried out by the University of Cambridge and Boston College found that the number of sick days taken by the 2,900 staff in the trial fell by about two-thirds.

Also, 39% of employees said they were less stressed.

Tessa Gibson, a senior accreditation officer at the Royal Society of Biology, said she would not want to go back to a five-day week – adding: “Weekends can be quite hectic, so it has been quite nice to have that extra day to see your friends and family, and then you get that extra day off during the week to do all your chores or to have that time to relax.

“It has made a big difference to my mental health.”

The COVID pandemic has meant that employers are having to find more flexible working arrangements in order to attract and retain staff, but not all businesses think a four-day week is the solution.

Jay Richards is the co-founder of Imagen Insights, which helps brands gather feedback from young people.

He said a four-day working week often leaves employees feeling like they have to squeeze more work into fewer days.

“I think a four-day week sounds good in principle but in practice how many companies are going to be able to support employees’ wellbeing if they are going from a normal five-day week and cramming that down into four days?

“We do a five-day week but we work 10am to 4pm, we shorten the days so the employees have that work-life harmony but they’re not actually shortening their week, which I think would put more pressure on them.”

The findings of the pilot scheme will be presented to MPs on Tuesday 20 February.