Keep Calm and Carry On – the sinister message behind the slogan that seduced the nation

It is on posters, mugs, tea towels and in headlines. Harking back to a 'blitz spirit' and an age of public service, 'Keep Calm and Carry On' has become ubiquitous. How did a cosy, middle-class joke assume darker connotations?

To get some sense of just what a monster it has become, try counting the number of times in a week you see some permutation of the "Keep Calm and Carry On" poster. In the last few days I've seen it twice as a poster advertising a pub's New Year's Eve party, several times in souvenir shops, in a photograph accompanying a Guardian article on the imminent doctors' strike ("Keep Calm and Save the NHS") and as the subject of too many internet memes to count. Some were related to the floods - a flagrantly opportunistic Liberal Democrat poster, with "Keep Calm and Survive Floods", and the somewhat more mordant "Keep Calm and Make a Photo of Floods". Then there were those related to Islamic State: "Keep Calm and Fight Isis" on the standard red background with the crown above; and "Keep Calm and Support Isis" on a black background, with the crown replaced by the Isis logo. Around eight years after it started to appear, it has become quite possibly the most successful meme in history. And, unlike most memes, it has been astonishingly enduring, a canvas on to which practically anything can be projected while retaining a sense of ironic reassurance. It is the ruling emblem of an era that is increasingly defined by austerity nostalgia.

I can pinpoint the precise moment at which I realised that what had seemed a typically, somewhat insufferably, English phenomenon had gone completely and inescapably global. I was going into the flagship Warsaw branch of the Polish department store Empik and there, just past the revolving doors, was a collection of notebooks, mouse pads, diaries and the like, featuring a familiar English sans serif font, white on red, topped with the crown, in English:

Few images of the last decade are quite so riddled with ideology, and few 'historical' artefacts are so utterly false

Related: Keep Calm and Carry On: The secret history

At Jamie's restaurants you can order pork scratchings for 4 and enjoy neo-Victorian toilets