National security threat

UK braced for attacks: North Korean 'sleeper' agents thought to be living in the UK

Intelligence chiefs fear they could launch cyber attacks on nuclear power stations and air traffic control centres in the hope of plunging the country into chaos.

MI5 and MI6 believe they entered using fake passports and posing as South Korean students.

They are thought to be part of a North Korean secret unit called the General Bureau of Reconnaissance, which conducts clandestine operations against “enemies of North Korea”.

They would have been acting on the orders of Kim Jong-un the country’s supreme leader.

The group, who are trained in assassinations, unarmed combat and sabotage, are part of an elite band of North Koreans who are allowed to leave the country.

It is believed that members of the unit were involved in the assassination of Kim’s half-brother Kim Jong-nam at Kuala Lumpur International Airport this year.