It’s the middle of the working day, and you’re at your desk. Someone is paying you to be there. But instead of the important business you’ve been tasked with, you’re reading the Guardian.

Screw the boss, you might say: I need a break. Unfortunately, though, it seems that even slacking at work may not be doing you any good. A comprehensive new study has shown that those who work very long hours face a 33% increased risk of stroke. Nor is this the first evidence of the health risks associated with overwork. No wonder you need to switch off for a bit.

Here’s the striking thing, though: the problem diagnosed here is not working harder: it is working longer. Much of the risk is associated with physical inactivity, and the study does not differentiate between the worker completing a spreadsheet and the one liking Facebook pictures of babies. The danger doesn’t lie in what you’re sitting there doing. It lies in the fact that you’re sitting there at all.

Oh dear, you fret, we’re all going to keel over. Then you turn to another story about the UK’s huge productivity problem and wonder how on earth we’re going to fix that. And then you think about maybe doing a spot of work before lunch.

It surely doesn’t take a presentation from Heather in HR to point out the absurdity of this. It is intuitively obvious that the longer you are expected to drudge, the less productive your drudgery is likely to be. And this isn’t just a hunch: there is a strong correlation between countries working longer hours and being less productive.

And yet we remain instinctive presenteeists. Anecdotes in the NYT investigation into Amazon’s working culture this week may have been extreme – no time for slacking off there – but certain elements sounded familiar for many of us, particularly the late night emailing. It is better to look busy and have a stroke, we feel, than to get things done then switch off.

How to fix this? Well, for an enlightened employer, it wouldn’t be so hard. Have an automated hometime reminder from the CEO pop up on every screen when 6 o’clock rolls around; ban email after 8pm except in genuine emergencies. When someone finishes a project early, reward them with the afternoon off.

At the moment, this utopian scenario seems unlikely. We remain in the grip of a political narrative that heralds the strivers and scorns the shirkers; David Cameron was reported to have made an opt-out from the working hours directive one of his goals in renegotiating our membership of the EU. And if our leaders aren’t willing to declare that the 1am email should go unanswered, it is hard to see anyone else doing so. They might start by reforming their own culture – for there are few workplaces more addicted to this macho nonsense than Westminster. But I don’t suppose any of them will be reading this. They’re all too bloody busy.