LONDON: When Harold Macmillan's ambition to take Britain into Europe was derailed by France's veto in 1963, he wrote in his diary: "All our policies at home and abroad are in ruins." Anyone involved in guiding British foreign policy in recent decades might feel the same way in the aftermath of the EU referendum. With one vote, the whole basis of British statecraft since the Suez crisis 60 years ago has been overturned.
That approach was designed to answer the famous challenge of Dean Acheson, then US secretary of state, who declared that Britain had "lost an empire and not yet found a role". Less remembered is what Acheson said next: "Her Majesty's Government is now seeking to enter Europe - wisely in my opinion."
When Macmillan first applied to join what was then the Common Market in 1961, his overriding aim was to ensure that Britain continued to wield global influence despite the loss of Empire.
Macmillan's strategy was to make his country a leading European power alongside France and Germany. What would ensure British pre-eminence was an asset that no other country could match: a uniquely close relationship with the United States.
Even better, Macmillan believed that Britain's two key alliances would be mutually reinforcing. There would be no need to choose between Europe and America, for Britain would have more influence in Washington if its voice was heeded in the chancelleries of Paris and Bonn - and vice versa.
The prize was so great that three Prime Ministers from both big parties - Macmillan, Harold Wilson and Edward Heath - doggedly pursued the goal of taking Britain into Europe.
The first two were thwarted by Charles de Gaulle's vetoes in 1963 and 1967 respectively, but Heath finally succeeded in 1973. From then onwards, every prime minister was guided by the overriding logic that Britain's role in the world depended on being a leading European power with a privileged voice in Washington.
Successive American presidents, from John F Kennedy to Barack Obama, played their allotted role in this doctrine, stressing how much they valued Britain's place in Europe.
Suddenly, all this has been cast into doubt. Whether and how Britain will influence Europe is open to question; so is the country's future relationship with the US. After all, just as London's old alliances with Washington and Europe were mutually reinforcing, the same logic dictates that to downgrade one is to undermine the other.
For the foreseeable future, the consuming task of the Foreign Office will be to cling on to as much as possible. At present, the UK has a permanent representative to the EU in Brussels, with a full complement of supporting diplomats, as well as the city's British embassy, which handles bilateral relations with Belgium.
Ironically, Sir Ivan Rogers, our permanent representative, will soon be busier than ever. He will have to begin the Herculean task of negotiating the terms of Britain's departure.
Instead of lifting its eyes to global horizons, British diplomacy will be overwhelmingly focused on the EU as the fiendishly complicated business of unwinding our membership takes precedence over all else. In parallel will come the almost equally formidable task of negotiating bilateral trade deals with the likes of China, India and America.
When all this is finally complete, in a decade or so, Britain will indeed have the opportunity to assume a global focus. But that invites the question: how interested will the world be in a post-imperial and post-European Britain? To adapt Acheson's phrase, Britain has relinquished a place in Europe in search of another new role.