“China has, I think, a very key role to play in terms of the pressure it can bring,” May said.“I have said this to President Xi, other have as well. We think that China has a role to play and we’d encourage China to do everything it can to bring pressure on North Korea to stop this.”

Pressed on whether the UK could back or be involved in military action, or seek to use cyber attacks to blunt North Korea’s efforts, May reiterated the need for joint action, with China at the centre.

“What is the UK doing? What we’re doing is working with our international partners,” she said.