In his 1930 essay “Economic Possibilities for Our Grandchildren”, John Maynard Keynes sought to counter the pessimism of the time by predicting that rising living standards and technological advancements would enable a 15-hour week by the beginning of the 21st century. “For the first time since his creation,” he wrote, “man will be faced with his real, his permanent problem – how to use his freedom from pressing economic cares, how to occupy the leisure, which science and compound interest will have won for him, to live wisely and agreeably and well.”

But though, as Keynes anticipated, living standards rose, the working week did not fall. Nearly 90 years after his essay, Britons work an average of 42.3 hours a week, the highest level of full-time hours in the EU (the lowest – 37.8 hours – is in Denmark). Productivity (output per hour), however, is 13 per cent below the G7 average. Overwork, leading to illness, absenteeism and low investment (among the worst in the G7), is emblematic of the new “British disease”.

A shorter working week has historically been a defining cause of the labour movement. Between 1900 and the Great Depression, the average Western working week was reduced from 60 hours to below 35. But in the post-war corporatist era, after the experience of mass unemployment, governments and businesses united to revere labour.

Until recently, the notion of a four-day week was largely confined to radical texts such as Alex Williams and Nick Srnicek’s Inventing the Future: Postcapitalism and a World Without Work and Rutger Bregman’s Utopia for Realists. But as the UK confronts the costs of overwork, the idea – part of what I have called Corbynism 2.0 – is moving from the fringes to the mainstream.

In 2017, the Green Party included a four-day week in its election manifesto, and last year the TUC backed the idea of a progressively shorter working week. A new 95-page report published today by the pioneering think tank Autonomy – The Shorter Working Week: A Radical and Pragmatic Proposal – represents the most detailed and persuasive case yet for a four-day week.

“This is a vital contribution to the growing debate around free time and reducing the working week,” shadow chancellor John McDonnell said of the report, signalling the Labour leadership’s endorsement. “With millions saying they would like to work shorter hours, and millions of others without a job or wanting more hours, it’s essential that we consider how we address the problems in the labour market as well as preparing for the future challenges of automation.” The left is resurrecting one of the classic socialist critiques of capitalism: that it makes humans unfree.

“The time we spend in work is neither natural nor inevitable,” the report notes. “Instead, the amount of time we spend in work is a political question.” Crucially, Autonomy emphasises that a four-day week is not just radical but credible. Research has long shown that, far from lowering productivity, shorter working hours increase it by reducing physical and mental illness, absenteeism, worker turnover and early retirement. There is no positive correlation between long worker hours and productivity: Germany is more productive than the UK (by 26.7 per cent) but works fewer hours on average; Mexico and Greece are less productive, but work more. And for those part-time workers who wish to work more, a four-day week would aid the redistribution of time.

Increased investment in technology, as well as a higher minimum wage to raise the cost of labour, would accelerate automation and make a four-day week conceivable. A recent trial by the New Zealand trust manager Perpetual Guardian proved so successful – higher productivity, reduced stress – that the firm is considering making it permanent.

Employers would be incentivised to improve the UK’s lamentable record of investment in machinery, robots and ICT: in 2017, Britain had just 33 robot units for every 10,000 employees, compared with 93 in the US, 170 in Germany and 154 in Sweden.

Greater productivity, the report notes, would eliminate the need to reduce wages in line with working hours. It argues for an extension of sectoral collective bargaining (the UK currently has the second-lowest level of coverage in Europe) to enable trade unions, businesses and governments to achieve “the correct balance between time and income”.

Further benefits of a four-day week include a reduced burden on healthcare services (poor mental health at work is estimated to cost employers £33-42bn, or 2 per cent of GDP, a year); greater environmental sustainability through a reduction in the number of commutes and an increase in low-carbon activities (such as walking or cycling instead of driving, and cooking with fresh ingredients rather than heating energy-intensive frozen food products); and increased gender equality by encouraging men to bear more of the burden of unpaid work and care.

To this end, Autonomy argues for the introduction in law of a new “UK Working Time Directive” (based on the European Working Time Directive) that would decrease annually with a medium-term target of achieving a full-time working week of 32 hours (or four days) by 2025.

The public sector would be used to pioneer lower hours without lower pay, new workers’ rights would give employees the option to take any rise in remuneration in the form of a reduced working week, the number of bank holidays would be increased from eight to 14 (in line with countries such as Spain and Malta) and policies such as universal basic income, universal basic services and sovereign wealth funds would be trialled to sustainably support life outside of work.

The history of progress is of once radical ideas – the right to strike, a free universal health service, a minimum wage – becoming orthodox. A four-day week could soon join them.

Autonomy's report The Shorter Working Week: A Radical and Pragmatic Proposal can be read in full here.