I'm assuming you don't live or visit the UK often, as that poster is everywhere and is used in various forms by huge numbers of companies. There is absolutely no political subtext to its use anymore.

It's a meme, the equivalent to using a cat image.

I live and work in central London.

Having seen the poster everywhere for a while now, it has been hard to avoid learning a bit about the image's history, including the recent hilarity with the EU trademark ( http://www.telegraph.co.uk/news/8785585/Battle-rages-over-Ke... ) and the image's organic growth in popularity from 2005 ( http://news.bbc.co.uk/1/hi/magazine/7869458.stm ).

I think it's funny to see people use things in apparent ignorance of their historical context; for example I was totally bummed that http://www.gophercon.com/ wasn't about the protocol.

    people use things in apparent ignorance of their
    historical context

The people behind the Go language are definitely aware of the gopher protocol.

A meme that Tumblr uses pretty frequently, at that.

It's actually pretty damn common in the US these days, too.

>only meant to be rolled out as a very last resort in the emergency situation that Nazis had occupied England.

Source? I'm reading that it was to be used if they experienced a "national catastrophe" or bombings with poison gas. I don't even know if it makes sense to print a propaganda poster for use after occupation.

This claim is not well-sourced (i.e. I exaggerated way beyond what we can prove is true.). Michael Balfour's 1979 book "Propaganda in War 1939–1945: Organizations, Policies and Public in Britain and Germany" discusses the slogan briefly in a footnote saying that it was considered too extreme vs. other possible slogans:

""By 3 August they had drawn up a shortlist of five slogans which was shown on that day to Hoare, who chose the three actually put into production (INF 720). The third poster 'Keep Calm and Carry on' [sic] was never displayed, as too obviously inappropriate to the actual conditions.""

  | I don't even know if it makes sense to print
  | a propaganda poster for use after occupation.

My thoughts as well. I'm pretty sure that the Nazis would do just fine generating their own propaganda posters had they occupied Britain.