FBI director Christopher Wray said China was the “biggest long-term threat to our economic and national security” and had interfered in politics, including recent elections.

MI5 head Ken McCallum said his service had more than doubled its work against Chinese activity in the last three years and would be doubling it again.

MI5 is now running seven times as many investigations related to activities of the Chinese Communist Party compared to 2018, he added.

The FBI’s Wray warned that if China was to forcibly take Taiwan it would “represent one of the most horrific business disruptions the world has ever seen”.

In response, China Foreign Ministry spokesman Zhao Lijian said British intelligence was trying to “hype up the China threat theory” and he advised the head of MI5 to “cast away imagined demons”.

He said the FBI director had also been “playing up the China threat to smear and attack China” revealing a “Cold War mentality” and urged him to stop making “irresponsible” remarks.

The first ever joint public appearance by the two directors came at MI5 headquarters in Thames House, London.

McCallum also said the challenge posed by the Chinese Communist Party was “game-changing”, while Wray called it “immense” and “breath-taking”.

Read more: BBC