One hundred companies in the United Kingdom (UK) have signed up for a permanent four-day working week for all their employees with no pay cuts, a milestone in the campaign to fundamentally change Britain’s approach to work, according to reports.

According to the Guardian, the 100 companies employ 2,600 staff – a tiny fraction of the UK’s working population – but the 4 Day Week Campaign group is hoping they will be the vanguard of a major shift.

Proponents of the four-day week say that the five-day pattern is a hangover from an earlier economic age. They argue that a four-day week would drive companies to improve their productivity, meaning they can create the same output using fewer hours. For some early adopters the policy has also proven a useful way of attracting and retaining employees.

The two biggest companies that have signed up are Atom Bank and global marketing company Awin, who each have about 450 staff in the UK. They have been accredited by the four-day week campaign, meaning they have demonstrated that they have genuinely reduced hours for workers rather than forcing them into longer days, the Guardian said.

Adam Ross, Awin’s chief executive, said adopting the four-day week was “one of the most transformative initiatives we’ve seen in the history of the company.

“Over the course of the last year and a half, we have not only seen a tremendous increase in employee wellness and wellbeing but concurrently, our customer service and relations, as well as talent relations and retention also have benefited,” he said.

In addition, the UK campaign is also coordinating the world’s biggest pilot scheme for about 70 companies, which employ about 3,300 workers, to adopt the four-day week in a trial with researchers at the Universities of Cambridge and Oxford, Boston College and think tank Autonomy.

In September, 88 per cent of those companies in a survey at the middle of the trial said the four-day week was working “well” for their business at that stage of the trial. About 95 per cent of the companies surveyed said productivity had either stayed the same or improved since the introduction.