The foundations of British foreign policy have been bulldozed by the events of the past six months: the EU referendum result and the upset White House victory of Donald Trump. Talk of a “special relationship” between Britain and the US has given way to confusion about how the UK can work with an unpredictable ally.

Prime Minister Theresa May has been forced to watch Nigel Farage, the interim UK Independence party leader, grab 15 minutes of fame with the president-elect. Yet it is premature to be despondent — Mr Trump’s victory represents opportunities as well as risks.

Whereas Barack Obama threatened to place Britain at “the back of the queue” for a trade deal if it left the EU, Mr Trump has made encouraging noises about brokering a new trade relationship. That is not within his sole gift — Congress will have its say — but it is a card to hold for the future.

For now, Mrs May’s priority must be to negotiate a free-trade deal with the EU, or a transitional arrangement to come into force after the two-year divorce talks are completed. Prematurely aligning with Mr Trump, who is openly contemptuous of the EU, risks alienating allies inclined to suspect the worst of British motives towards Europe. The UK needs the closest relationship possible with the bloc to protect its economy. A prospective trade agreement with Mr Trump’s America is no compensation for a bad Brexit.

Another unknown is how Mr Trump will conduct foreign policy. He may well temper his outrageous statements from the stump. But the relationship with the UK will be dictated by Mr Trump’s priorities and strategy. His views on Russia, the Iran nuclear deal and Nato conflict with British interests. The Foreign Office hopes to steer Mr Trump towards more conventional positions — as revealed in a leaked cable from Washington — but it would be unwise to assume he is open to counsel, especially from foreigners.

The prime minister is tentatively hoping to find a middle way. In her first major foreign policy speech, Mrs May said on Monday that the UK will not resile from being a staunch defender of liberalism and globalisation, but it will need to “adapt to the moment and evolve its thinking” in light of Brexit and Mr Trump’s victory. This is sensible, but it will require deft diplomacy to manage the backlash against globalisation on both sides of the Atlantic. The Italian referendum in December and next year’s elections in France and Germany underline the perils ahead. The ghosts of nationalism are stalking the continent.

Mrs May should keep in mind that the special relationship with the US has always been based not just on shared interests, but on shared values. For all US administrations after 1945, Britain’s importance as an ally has tended to be in proportion to the role it plays in Europe: building support for US foreign policy positions, identifying with its values and acting as a channel for American economic interests. Neither Mr Trump nor Brexit changes that.

The president-elect should not just be judged on his coarse rhetoric but on his actions in office. Since his victory, he has signalled a retreat from some of his more extreme positions. If he continues to do so, and sets proper store by traditional alliances, then the UK will have an important role to play.

Mr Trump will not be an easy partner. He may well take decisions — both at home and abroad — that will unsettle a British government committed to liberal, democratic values. Palmerston’s dictum that nations have no permanent friends or allies, they only have permanent interests is no longer sufficient. British values still matter.