With its simple five word exhortation it has become symbolic of the British spirit of steady defiance in the face of Nazi aggression.

So much so that its Keep Calm and Carry On slogan has in recent years been reproduced on everything from mugs and coasters to T-shirts and tea towels.

But in fact this evocative red and white poster was banned by Britain’s wartime government and did not see the light of day until years later.

Now, however, the only known photograph has been discovered of one of the few posters which survived the Government ordered destruction being used for its intended purpose.

It shows scientists working at a Government weapons research laboratory in Bedfordshire with the poster hanging on the wall behind them, despite the ban.