Seventy companies and 3,300 employees are taking part in what is being claimed as the world's biggest trial of the four-day work week with no loss of pay for workers.
The trial will run for six months and is being coordinated by the 4 Day Week Global campaign in partnership with UK thinktank Autonomy and researchers at Cambridge University, Oxford University and Boston College.
The pilot is based on the 100-80-100 model, where employees get 100% of the pay for 80% of their normal working week, in exchange for a commitment to maintain at least 100% productivity.
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Similar pilots being coordinated by 4 Day Week Global are occurring in the US, Canada, Australia, and New Zealand.
The UK pilot has drawn participating firms from education, banking, healthcare, financial services, tech and media, construction, retail and more, according to 4 Day Week Global.
Joe O Connor, CEO of 4 Day Week Global, says the UK is at the "crest of a wave of global momentum behind the four-day week". He argues the "great resignation" beginning in early 2021 proved that better outcomes can be achieved by working "shorter and smarter".
"As we emerge from the pandemic, more and more companies are recognising that the new frontier for competition is quality of life, and that reduced-hour, output-focused working is the vehicle to give them a competitive edge," said O'Connor.
The pilot comes as firms decide whether staff must return to the office, which some tech CEOs reckon is over as a location for work, or whether they can work remotely, indefinitely.
Researchers in the UK pilot will assist participating companies measure productivity and worker wellbeing during the pilot, and provide a confidential report after its conclusion.
Charity Bank, a small UK bank owned by charities and trust funds, is participating in the pilot. It claims to be the first UK bank to reduce its work week from a standard 35 hours to 28 hours for the same pay and benefits.
"The 20th-century concept of a five-day working week is no longer the best fit for 21st-century business," says Ed Siegel, CEO of Charity Bank.
"We firmly believe that a four-day week with no change to salary or benefits will create a happier workforce and will have an equally positive impact on business productivity, customer experience and our social mission."
Siegel says that by the bank valuing productivity over time spent, it hopes to remove any sense of barriers to promotion and progression felt by part-time staff.
"We anticipate that the shorter working week will also help us attract a more diverse workforce and encourage people who would previously have been unable to commit to the standard five-day working week to join us," he said.
Other UK 4-day working week participants include games developer Hutch, telecoms services firm Yo Telecom, Playyen's Fish and Chips in Norfolk, Salamandra animation studios, and Timberlake Consultants.
Similar trials have taken or are taking place in Iceland, Japan, United Arab Emirates, Scotland and Spain.
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Some employers are not keen on more flexible-working arrangements. Tesla chief Elon Musk last week told employees in a leaked email that they must return to the office to work at least 40 hours per week or leave the firm.
Iceland's four-day week trials between 2015 and 2019 were deemed by Iceland's Association for Sustainable Democracy and Autonomy an "overwhelming success", with workers reporting an improved life-work balance and employers reporting increased productivity.
Microsoft's 2019 trial of a 4-day work week with 2,300 employees in Japan created a 40% rise in productivity, measured by sales per employee. Employees were given every Friday off for one month with no reduction in pay.
Microsoft said workers crammed a week's worth of work into four days by keeping meetings shorter, switching to remote meetings, or cutting out meetings deemed unnecessary.