Invited in 1962 to give a speech at West Point, the US military academy, Dean Acheson rehearsed a mostly anodyne argument on Britain’s relationship with America. It was only via a throwaway remark that the former US Secretary of State put a metaphorical bomb under the British establishment. “Great Britain has lost an empire but not yet found a role,” he said. “Attempting to be a broker between the United States and Russia, [the UK] has seemed to conduct policy as weak as its military power.” For half a century, British foreign policy has lived in the shadow of that remark. When I worked at the Foreign Office during and after September 11 2001, senior officials would recall it constantly. Yet over the past week, Britain may have finally emancipated itself from Acheson’s curse. As parliament confounded our Prime Minister, and Barack Obama, paying close attention, said he would seek the approval of Congress for a military strike on Syria, perhaps our role was clarified: to encourage caution in American presidents, something we spectacularly failed to do over Iraq a decade ago.

