KCNA KCNA/Reuters
Mo Nabbach told the London Evening Standard newspaper that two officials from the Stalinist state's mission took pictures of the M&M Hair Academy in Ealing, west London.
They then ordered him to remove the "disrespectful" poster, he said.
The poster featured a large picture of Kim's distinctive short-back-and-sides hairdo with the slogan: read: "Bad hair day? 15 percent off all gent cuts through the month of April."
"I told them this is England and not North Korea and told them to get their lawyers," the newspaper quoted Nabbach as saying.
"The two guys were wearing suits and they were very serious. It was very threatening."
Nabbach, who is also a fashion photographer, said he had since removed the offending picture.
Police confirmed that they had stepped in to resolve the issue.
"Officers spoke to both parties involved and no offence was disclosed," a Metropolitan Police spokesman told AFP.
There was no immediate response from the North Korean embassy, located in a suburban London house less than two miles (three kilometres) from the salon.
The Kim family has ruled the country for more than six decades with an iron fist and a pervasive personality cult.
Kim Jong-Un's haircut is strikingly similar to that of his grandfather Kim Il-Sung, reinforcing efforts by the young leader to project himself more in the image of the state's founder leader than his father Kim Jong-Il.
