A string of small British firms have switched their workers over to a four-day week, the Guardian can reveal, amid mounting political interest in the idea that working less could deliver higher productivity and better balance between life and work.

A lingerie manufacturer, a lighting design firm and a landscape architect are among a wave of employers experimenting with giving staff three days off per week, for no less pay. The Wellcome Trust, the largest employer in Britain to so far consider a four-day week, is thinking about doing a trial for its 800 staff.

Growing calls for a shorter working week are being opposed by the Confederation of British Industry on the basis that more flexibility, not less, is needed.

But the shadow chancellor, John McDonnell, has commissioned a study into its value from the economist Robert Skidelsky, and the Scottish National party is due to debate a motion next month calling for a review which could lead to the introduction of the four-day week in Scotland.

In the last six months, companies switching to a four-day week include Synergy Vision, a 45-employee medical communications agency, Elektra Lighting, a lighting design company, Lara Intimates, which makes underwear, and the Intrepid Camera company, which makes and exports photographic equipment.

“It has been a beautiful six weeks of having a long weekend,” said Neil Knowles, a design consultant at Elektra, which switched its 10 staff to a shorter week in January.

“Two days out of seven is just enough to recover from a stressful week. Three is enough to recover and have extra time to do something else. It almost feels as if work is interrupting the weekend rather than the other way round.”

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Maxim Grew, at Intrepid in Brighton, said the switch has ended “Friday afternoon fatigue” and increased morale and energy levels among staff with a feeling that every hour counts, leading to productivity boosts. He said people have quickly adjusted to using the extra time off.

“I am learning French, Rocco has joined a theatre group, Hugo is spending more time doing carpentry and Sam is building a robot,” he said.

Vanessa Ross, the owner of Arc Landscape in Surrey, said her team had used the time to volunteer, look after dependent family members and teach.

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The idea of a four-day week has shot to prominence in recent months, for economic, social, health and technological reasons.

Overwork results in thousands succumbing to stress or depression each year, according to the Health and Safety Executive; long working hours make parenting and family care ever trickier to juggle; technology, meanwhile, threatens to transform the demand for labour over coming decades.

Despite this, Britons work more hours a week on average than they did in 2011 – and research shows two-thirds would like to reduce the amount of time they spend in the office.

One of the biggest experiments so far into the effect of the four-day week was carried out at Perpetual Guardian, a finance company in New Zealand. It claims productivity has increased.

Its chief executive, Andrew Barnes, said: “This is an idea whose time has come. 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.”

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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.

Billy Jenkins, a middle manager at Synergy Vision, said: “It has caused a little tension in the household, as my partner works five days a week and seems to come up with a wishlist of errands or chores that need doing on my day off. It’s also hard to shake off the feeling that I should be working, and it has taken time to feel more comfortable using the time as my own.”

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