A council that has been trying out a four-day week for office workers and bin collectors is to defy ministers and press ahead with its new working pattern, it has announced. Refuse collectors for South Cambridgeshire district council will start a new shift rota from next week, which means bins will not be collected on Mondays as the Liberal Democrat-led council extends its trial of the compressed working week. Last week Lee Rowley, the minister for local government, wrote to the council, saying: “This experiment should end.” The letter was an escalation after the government said in June it was opposed to four-day weeks in town halls. In an intensifying standoff, Rowley has now warned the council could face court action if it presses on and told it to “end your experiment with taxpayers’ money immediately”. He said: “We are currently considering other financial options available to us regarding ending ‘four-day weeks’ in the local government sector should it remain necessary to do so.” But Bridget Smith, the council’s leader, said on Wednesday the four-day week would continue until the end of its trial period after it boosted the number and quality of job applicants, saving more than £550,000 a year in agency worker costs and allowing it to fill nine posts that no one previously wanted. “We have consistently said that this is an evidence-based trial to see whether a four-day week can improve our critical recruitment issues,” she said. “Not being able to fill vacant posts – especially in our planning team – is disruptive to services for our residents. We need the trial to run for its full planned length, until the end of March, to gather data and assess whether a difference has been made.” Joe Ryle, the director of the 4 Day Week campaign group, welcomed the decision. “Nine in 10 councils are struggling with job recruitment and retention and a four-day working week could be the answer,” he said. “Wherever a four-day week has been implemented, it’s been a win-win for workers and employers. Productivity improves and so does the wellbeing of workers.” Dozens of private companies have experimented with paying workers the same money for fewer hours. A trial among 61 firms reported back in February, with 18 making a permanent changeand the idea is now spreading to the public sector. Earlier this month the Scottish government announced it would start its four-day working week public sector pilot by the end of 2023 “to assess the wellbeing, environmental, and productivity benefits”. But the Westminster government is strongly opposed. Rowley said South Cambridgshire’s claim its trial so far had been a success was “somewhat curious” and said it was missing council housing targets, suffering worsening performance at its call centre and had missed targets for rent and council tax collection and for processing housing benefit claims. He said: “The role of a council is to secure continuous improvement. The removal of up to a fifth of the council’s operating capacity seems unlikely, in aggregate, to be able to support this.” The council gave explanations for its performance in those areas, with Smith saying: “Any statistic taken in isolation and without at least some explanation simply does not give the full picture.”