As usual, Mike Pompeo was brutally frank. Speaking in London last month, the US secretary of state warned that future bilateral intelligence sharing would be at risk if Britain allowed the Chinese telecoms giant Huawei access to its new 5G rollout. “The US has an obligation to ensure the places where we operate [are] within trusted networks, and that is what we will do,” he said.

The issue might appear arcane. But Pompeo’s threat, which Donald Trump will reiterate during his state visit, beginning on Monday, sent a chill through the diplomatic, defence and security establishment. In an age of rapidly diminishing influence, Britain still prides itself on its intelligence gathering, counter-terrorism and counter-espionage capability, as well as agencies such as GCHQ and its new offshoot, the National Cyber Security Centre.