When the UK's Labour Party set out proposals for a four day week in their manifesto in 2019, it faced a lot of criticism from politicians in opposing parties and businesses.
It was argued that if the proposals sought to introduce a four day working week, but did not reduce the pay, then businesses would end up having to pay 20-25% more for less productivity. If the position was that people take pay cuts and do a four day week, it was argued that this would negatively affect the poorest in society as they would benefit from less income. Additionally, it would hamper people's abilities in gaining opportunities. 
The idea was again entertained by a cross-party group of MPs in June 2020, urging the Chancellor, Rishi Sunak, to consider the proposal. There is no movement on the position.
A government spokesperson suggested that for private companies, it was not for the government to dictate working patterns, and the civil service already has flexible working patterns.