Britain’s stunning referendum vote to leave the European Union has thrown a cat among the pigeons, not least in Washington, where it is feared that the “Brexit” could scupper its anti-Russian policy.

That tacit policy is a foundation of the postwar international order whereby Washington – thanks to its trusty British acolyte – has been able to exert hegemony over Europe. Nearly seven decades of American transatlantic domination are at risk of crumbling.

The unscheduled, hasty visit by US Secretary of State John Kerry to Brussels followed by London on Monday is a sure sign that Washington is alarmed at the historic decision by the British electorate to quit the EU – after 43-year membership of the bloc.

“Kerry urges Britain, EU to manage their divorce responsibly,” was how American news outlet ABC reported the diplomat’s detour. The outlet went on to say with a pretense of chivalry that Kerry’s concern was “for the sake of global markets and citizens”.

More to the point, Washington’s perplexity is specific and self-serving. In particular, the loss of British influence inside the EU will impact on Washington’s carefully constructed policy of trying to isolate Russia. American objectives to isolate Russia go much further back than the past two years over Ukraine. Indeed, one can trace the anti-Russia policy to immediately after the Second World War, a policy that was intimately shared by the British establishment, as expressed by Winston Churchill in his famous 1946 “Iron Curtain” speech, marking the onset of the Cold War against the West’s erstwhile wartime Soviet ally.

Former US ambassador to Russia, Michael McFaul, gave full expression to these fears in an opinion piece in the Washington Post at the weekend. The headline read: “How Brexit is a win for Putin”.