It was originally a Second World War rallying cry to all Britons, but 70 years later the 'Keep Calm' slogan is now the subject of a long-running legal copyright dispute.
The wartime message has in recent years become an iconic national slogan after the phrase appeared on posters, books, mugs and other merchandise.
But 'Keep Calm' - originally produced by the government's Ministry of Information - has since been trademarked by an entrepreneur who has claimed a monopoly on the famous phrase - and prevented anyone else from repeating it.
Businessman Mark Coop, from Surrey, has since been branded 'deplorable' for banning other traders from using the slogan.
He has registered a trademark for 'Keep Calm' with the European Union, sparking a furious response from the book store director who says he first brought the phrase to the public’s attention.
Stuart Manley, a second-hand book store owner in Alnwick, Northumberland, found one of the original wartime posters in a box of auctioned books in 2000.
After placing the poster, with its white writing on a red background and unmistakeable George VI crown, in his shop window and receiving dozens of requests for reprints, Mr Manley began selling copies in his shop.
He had checked with the Imperial War Museum that the copyright had expired before selling copies of the poster.
Barter Books in Alnwick has since sold 100,000 posters after he began the process which made 'Keep Calm' a global phenomenon.
Entrepreneur Mr Coop, from Surrey, began a legal dispute when he launched a bid to trademark the phrase.
After selling mugs, aprons and other items with the design from 2007 and failing in an initial bid to get it trademarked in the UK, he gained an EU trademark for the slogan and has claimed a monopoly on it since.
He has enforced his rights to trademark ownership by stopping anyone on eBay from selling products with the slogan.
Mr Manley's legal challenge against Mr Coop's trademark has been supported by a petition signed by 2,600 people and Mr Manley’s is hoping that the copyright dispute will see a resolution in the new year.
Mr Manley, 70, had previously accused Mr Coop of 'pretty deplorable behaviour' in trademarking the iconic slogan.
Mr Coop defended his position by insisting that he simply trademarked the message first, and that he has banned other traders from using it 'to protect his own interests'.
Today Mr Manley insisted that ownership of the phrase should not belong to entrepreneur Mr Coop, who trademarked it in April last year.
Mr Manley told Yahoo! News: "The reason we didn't copyright it is we didn't think we had the right to do so.
"Our stance was that as long as people recognised us as the source, we allowed them to use it.
"We don't really feel that the phrase should belong to anyone, and certainly not to him."
In recent years the 'Keep Calm' message has appeared on everything from tea towels to mugs, t-shirts and even mousemats.
The phrase has permeated every part of popular culture, and was even aped by Premier League footballer Dimitar Berbatov when he showed a t-shirt saying, 'Keep calm and pass me the ball' after scoring last month.
But Mr Manley claims Mr Coop monopolised the phrase after it became a global phenomenon by requesting one of his own prints and then removing the copyright.
He added: "By the time Mr Coop got involved the phrase was already established all over the world. He was one of the people who bought a copy of the poster from us.
"However, he snipped the name off and used the copyright for his own purposes.
"Since then it has been in the hands of intellectual property lawyers who have been tossing things back and forth.
"His defence is that he was the first one to trademark it - I consider that ethically wrong, but also think that no-one should trademark it."
The long-running legal saga has seen Mr Manley hire a trademark lawyer in a bid to overturn the EU decision.
Speaking in late 2011, Mr Coop said: "Barter Books didn’t see the opportunity that I saw, and I think they were rather naive in failing to register the domain name or trademark the slogan.
"I have made numerous efforts to make amends with them and work together, but they didn’t want to know.
"All I am trying to do is protect my business and my livelihood and prevent other people jumping on the back of what I’m doing."