Four day weeks could cause employees to overwork
Although a four day week has been welcomed as creating a more productive and happy workforce, there are downsides to the implementation of a four day week. If individuals work a four day week, and have the same workload, they are more likely to work longer hours during the four days to achieve their deadlines. If they are unable to meet their deadlines, they are likely to be stressed about their work over their days off, and not fully be able to enjoy their time off. It is argued that the longer hours within the four days or the stress over not being able to meet deadlines is not worth the one extra day off. 
On average, a British employee working full time works 42 hours a week, with two billion hours of unpaid overtime. Over half a million workers suffer from work related mental health conditions, with 15.4 million days lost to work related stress.  Being able to redistribute hours away and engaging in more leisure time, would stop individuals from being overworked, giving an overall better quality of life. The founder of Unchartered had encouraged more rather than less working hours during the pandemic. After a few weeks, it became apparent that staff were struggling with balancing work, meetings and home-schooling, and so a four day working week was introduced. It was found that employees seemed more engaged and refreshed. In another firm it was found that working compressed hours focused people more and things were done more efficiently, with meetings being streamlined.