The Special Relationship has seen more special days. Earlier this year, President Trump delivered his verdict: ‘How is the relationship? It’s the relationship where, when we asked them for help, they were not there. When we needed them, they were not there. When we didn’t need them, they were not there. And they still aren’t there.’

Trump was referring to divisions between the US and UK over the wisdom and conduct of the war in Iran. (Even amid a spat, though, he can dish out praise. Just this week, following the arrest of five men outside RAF Fairford, used by American bombers to strike Iran, the President said the UK authorities had done an ‘amazing job’.) But his remarks landed at a moment of divergence in the US-UK relationship that extends well beyond Iran. Washington has imposed and reimposed tariffs on Britain. Last year the UK paused intelligence-sharing that could have assisted American strikes against suspected drug boats in the Caribbean, which London views as illegal. Trump has branded the deal to hand the Chagos islands to Mauritius an ‘act of great stupidity’.

All this has resulted in a great deal of hand-wringing about the resilience or otherwise of the Special Relationship. There is a great fear of change, given how historically close the relationship is, particularly  in intelligence. The Special Relationship’s entire origin story, in fact, is a cryptographic exchange over German and Japanese codes at Bletchley Park in 1941. Eighty-five years later, the intelligence connection between the US and UK remains central; having the same set of eyes and ears means you see the world similarly and act accordingly.

Britain is the decidedly junior partner. When push comes to shove, the CIA wins out

Britain is the decidedly junior partner. When push comes to shove, the CIA wins out

But might gathering political headwinds blow hard enough to damage it? To understand how – or if – the intelligence partnership might come apart, it is helpful to examine how it actually works.

This is the subject of my new novel, London Station, in which I imagine a scenario where the CIA and MI6 begin spying on each other. There is a historical precedent for this. Prior to the second world war, Britain intercepted US diplomatic traffic and conducted influence campaigns on American soil. In one instance, British spies drew up and disseminated a supposed Nazi map depicting Germany’s vision for a partition of South America in a bid to frighten US policy-makers into entering the........

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