After a forgotten WW2 propaganda poster was discovered in 2000, it found an astounding new resonance in 21st-Century Britain – becoming an endlessly memeable template that is both cherished and mocked.

In the spring of 2000, a forgotten World War Two-era British propaganda poster was rediscovered in a dusty box at Barter Books, a second-hand bookshop housed in a former Victorian railway station in Alnick, Northumberland. The red poster and its bold, unadorned message beneath a Tudor crown, Keep Calm and Carry On, would resonate with a world far removed from wartime Britain, sparking a viral design trend and becoming one of the 21st Century's most recognisable and repurposed cultural slogans.

The poster, commissioned by the British Ministry of Information in 1939 as part of a three-part series to bolster public morale amid the threat of war, was never officially released, and had rarely been displayed. Dr Daniel Cowling, senior historian at the National Army Museum, London, says the Ministry of Information often used posters, cinema, radio, books and pamphlets to influence public opinion during World War Two. In addition to the Keep Calm poster were two others, which carried the slogans Your Courage, Your Cheerfulness, Your Resolution Will Bring Us Victory and Freedom is in Peril. Defend it with All Your Might.

"On the eve of the war, it was widely accepted that bombing raids would lead to the rapid and complete breakdown of society", Cowling tells the BBC. "Keep Calm and Carry On was designated as a specific response in their aftermath. It played upon stereotypes of British stoicism in the hope of restoring order amid the expected chaos."

The other two posters were plastered across railway stations, factories, and shop windows, but received a tepid response. Mass Observation surveys suggested that public response to the wider "Home Publicity" poster campaign was overwhelmingly negative, says Cowling. British towns and cities did experience heavy bombing raids, but there was no breakdown of society. "Rather, many civilians responded with resilience and spirited togetherness. [So], the Keep Calm poster would have seemed rather patronising to some British civilians," he explains.

The iconic poster, which was designed by British illustrator Ernest Wallcousins and of which about 2.5 million copies were printed, was held back. It remained largely unseen by the wider world, as most copies were pulped in 1940 to conserve paper for the war effort. A few copies survived, tucked away in archives, including the one in the box at Barter Books.

Stuart and Mary Manley, owners of Barter Books, were taken by the poster. "We decided to have it framed and put it up in the bookshop. We had no idea of what it would become. Mary resisted the idea of having copies printed, so I had to have them done secretly. The popularity of the copies soon changed her mind," Stuart Manley tells the BBC.

For the first few years, the poster's popularity remained purely regional, confined to bookshop visitors. The explosion began when Guardian journalist Susie Steiner included it in a 2005 article on her 10 favourite design items. "Our staff spent the next month packing........

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