I didn't read the article, but I'm assuming all of it is here, and I'm wondering if workers' hours per week are going to be reduced or if they're going to be kept the same but with longer shifts per day.
Either way, I've worked 40 hour weeks spread out between both 4 and 5 days, and I much preferred only having to work 4 days even if I had to work 10 hours/day. It's definitely nice to have three days off a week. I assume the UK workers are going to be putting in fewer hours, else there wouldn't be a news story about it, and if that is indeed the case more power to them. Most people in this world are worker bees (myself included), and a lot of us hate our jobs, our bosses, coworkers, and/or the company we work for. With technology being as advanced as it is, a lot of work could be done by robots--and should be if it isn't already.
It then comes down to a question of whether to keep paying existing employees their regular salary, and I suspect a lot of companies might have a problem with that.
"They argue that a four-day week would drive companies to improve their productivity, meaning they would achieve the same output in fewer hours."It is, as OP said, also said that there won't be any pay cut. I would say it really depends on the industry whether it is possible or not. There are sometimes just some logistical hurdles to cut a week down from five or even more days to less days, respectively. The articles I just went through mostly refer to the well-being aspect and the chance to attract new talent.
I have seen articles in the past for such initiatives for other countries as well, and I recall that it was often said that the work would still have to be done for the week. So to say, the deal being that if the work is done on Thursday, people can take Friday off. This would go into the direction what you mentioned, work 10h/day if you please and then take three days off. Whenever possible, I would advocate such a model as well.
I have been in a job where I was completely free to choose to work between 6 hours and 12 hours a day. That was back at the time when I was in my early 20s. A certain goal was set for the week and we were free to choose (unless there was an urgent deadline) how to go about the workload for the week. 6 days were possible, starting as early as 5 AM and finishing as late as 9 PM. Of course one could argue that the productivity decreases when working days get longer and longer, but first, you can really get used to it as you know that we are just talking about a three day work week potentially and you have plenty of time to recover, if necessary. And second, it really depended back then on the work that needed to be done. We had a mix of less intellectually exhaustive work (engineering experiments where stuff just had to be prepared according to plan), and more exhaustive stuff (actually coming up with the plans). I can tell you that most of the people arrived at 5 AM in the morning and left at 5 PM in the afternoon and still had a happy face. It was such an amazing and diverse group that I was working with back in the days. Very well educated mothers who could organize a nanny for their children much easier (because just three days a week), lots of students who were literally able to take a 70% job besides their studies (that was how I got started, but I went full time), but also lots of engineers in their 70s who weren't able anymore to go a full and stressful distance.
From what I can tell, our productivity level back at the time was always on point. I did that job for almost 10 years and then I went abroad. I have ever since been a strong proponent for way more flexible working hour models. Application numbers for that company always were through the roof back then and the diverse set of people on my team also showed that there are crazy different circumstances people are coping with, and they have all been willing to work hard, but had to sort out all kinds of problems in order to make their weekly schedule fit their life circumstances. Children, taking care of parents ( for example on dialysis days, their own health issues, studies, shared custody, desire for individual freedom, time consuming/extravagant hobbies, etc. the list goes on).
Most people really aren't lazy. Many bosses who complain are also often not very good at defining goals and the respective guidelines. Defining goals and guidelines can actually be a hard thing, it is not always trivial. All too often the blame for lack of success is shifted onto the workforce. The company I worked for back at the time had frequent meetings involving their employees with the objective to improve the definition of goals. After some time everyone developed a feeling for the time and effort that is probably required to get to a certain desired point/output. Of course it didn't always work out perfectly and we needed more time and those who were able pulled off way more hours a week then, but even then our boss paid the extra hours in many of the cases unless we really fucked up.
If the system and the whole environment is set up the right way, and a way that allows for the system itself to evolve over time, flexibility can be an enormous contributing factor to productivity.