The Five Eyes has for decades been the most important intelligence-sharing network in the world. The US and its allies share extremely sensitive signals and human intelligence in addition to co-ordinating on operations. The CIA-led Pine Gap satellite station in central Australia, which is the most important site for collecting intelligence about China, is just one example of the intimate intelligence relationship.

Dennis Wilder, a former CIA official who was the top editor of the US president’s daily intelligence briefing, said the Five Eyes was “by far the most successful intelligence-sharing arrangement in world history”. He noted that the partnership emerged when American and British code breakers worked together to break German secret communications during the second world war, and was expanded to include the other allies in 1956.

“Any disruption in these decade-old understandings would be met with cheers from our adversaries in Moscow, Beijing, Tehran and Pyongyang,” said Wilder.