I think an accepted four-day work week in the UK is entirely possible within the decade.
Any business that can measure its employees' work output on performance will be able to have increasingly better insight into the quantity of work produced by each employee. If management can compress 5 days into 4, I'm sure they will, although for the employees that will probably come at the cost of a decrease or at least stagnation in wages for a few years.
Increased automation from 'AI' (loosely used) software will also play a big role in making some services entirely obselete. Chatbots, text and voice, will remove the need for any kind of call service teams, for instance.
As for the 24/7 supermarkets @Briefcase mentioned, it's now a matter of time before Amazon or similar manages to create a same/next day grocery delivery service good enough that will render the need for 24/7 supermarkets irrelevant.
However, I think by far the biggest point to make here is that a four-day work week would be so beneficial to consumer brands and businesses that I could see a major push for it to happen.
It's an extra day that could be spent browsing Facebook, buying from Amazon or reading news websites. It's a golden ticket for consumer capitalism.