Pensions Minister Emma Reynolds lashed out at the Public and Commercial Services (PCS) Union over its call for government workers to get a three-day weekend to facilitate ‘one day of chores, one day of fun and one day of rest’.

The PCS argues that the plan would save the taxpayer more than £21 million a year, halve staff turnover and cut the rate staff call in sick by almost two thirds.

Her remarks highlight a growing Government split over the issue. Ms Reynolds’ Treasury boss Rachel Reeves is opposed to a four-day week, but other ministers including Deputy Prime Minister Angela Rayner support the change.

General secretary Fran Heathcote said the study suggested any opposition to employees working a four-day week was ‘purely ideological’ because the arrangement has ‘financial benefits too.’

But Joe Ryle, director of the 4 Day Week Campaign, said: ‘Emma Reynolds comes off like a Tory minister stuck in the past.

‘The truth is that the 9-5, 5 day working week is outdated and no longer fit for purpose. It was invented 100 years ago and we are long overdue an update.

‘As hundreds of British companies and one local council have already shown, a four-day week with no loss of pay can be a win-win for both workers and employers.’

Whitehall officials are campaigning for Defra to carry out a pilot so that managers can assess the arrangement.

Statisticians within the department who are members of the PCS say the Government could save £21.4 million from the move, branding it ‘essential for a happy and healthy life’.

That figure is based on Institute for Government modelling of the year 2016-17 and updated to reflect a rise in salaries, staff numbers and turnover since then.

In a survey of more than 1,200 members carried out by the PCS as part of its research, 80 per cent of respondents said the change would give them health and wellbeing benefits.

General secretary Fran Heathcote said the study suggested any opposition to employees working a four-day week was ‘purely ideological’ because the arrangement has ‘financial benefits too.’

‘Why else would an employer stand in the way of progress?’ she said.

‘Our members are resolute in their belief that a four-day week is critical to attaining a good quality of life, improving their health and wellbeing and helping them to meet caring responsibilities, while all the time increasing their productivity.’

Director of the 4-Day Week Campaign Joe Ryle, who wrote a foreword to the research, said the ‘time has come’ to trial the arrangement in Whitehall.

‘As hundreds of British companies in the private sector have already shown, a four-day week with no loss of pay can be a win-win for both workers and employers,’ he said.

A Defra spokeswoman said there were no plans for a four-day week.

The Government last week dropped official concerns about South Cambridgeshire District Council’s four-day week after the authority faced opposition from the previous Tory administration.

But there has been kick-back against the idea. Last month civil servants will have to spend at least three days a week in the office after senior Whitehall officials recommitted to rules on working from home.

Under the previous Tory government, civil servants were told to spend 60 per cent of their time in the office or on official business, rather than at home.

Following July’s general election, it was reported that newly-appointed Labour ministers were quietly ignoring the rules in a ‘less dogmatic’ approach towards staff

But Whitehall chiefs have now made a fresh commitment to the 60 per cent target after deciding the guidance should not change.

Cat Little, permanent secretary at the Cabinet Office, was revealed to have written to other heads of departments yesterday to reconfirm the three-day-a-week instruction.

It appears to be a victory for the Chancellor after she put herself at odds with Cabinet colleagues by hailing the benefits of staff working together in an office.

Ms Reeves  said she ‘leads by example’ by turning up to her Treasury workplace and said staff benefitted from ‘coming together’ to work ‘collaboratively’.

This contrasted with the stance taken by Business Secretary Jonathan Reynolds, who had criticised a ‘culture of presenteeism’ in Britain’s workplaces.

He also insisted a default right to flexible working would boost productivity and hit out at the ‘bizarre’ Tory approach of ‘declaring war on people working from home’.