Donald Trump's election victory could pose diplomatic difficulties for the "special relationship" between the UK and United States.
Theresa May has said she will speak to the new leader of the US as soon as possible after the election result is known in an effort to maintain the strong transatlantic link.
But experts have warned that the UK should not expect any favours from Mr Trump, who has campaigned on a promise to "Make America Great Again" and criticised free trade deals signed by the US.
The special relationship - dating back to the Second World War - is treasured by all British prime ministers as a mark of close alliance with the world's most powerful country.
After every change at the White House, it is a key part of UK diplomacy to ensure the new president is willing to reaffirm its continuation.
Although the US has allies around the world, London believes that the special relationship gives Britain enhanced access in terms of military co-operation and intelligence sharing.
Ministers have insisted that the UK would remain "the closest of partners" with the US, whoever was in the White House.
After the Brexit vote, the prospect of a UK-US trade agreement would be a major boost to the British economy and Mr Trump may be more receptive than Barack Obama, who said Britain would be at the "back of the queue" for a deal.
Mr Trump's trade adviser Dan DiMicco said the UK would get priority status because it was America's "friend" and was quitting the European Union for good reasons.
But Mr Trump has struck a decidedly protectionist tone in his talk on trade, criticising deals including the North American Free Trade Agreement (Nafta), indicating that negotiations may not be straightforward.
Mr Trump has also criticised Nato, leading to alarm in Europe about the prospect of a US commander-in-chief who was not fully committed to the alliance.
And his controversial comments on women and Muslims could also colour his relationship with senior members of the British Government.
As home secretary, Mrs May told a Commons committee last year that Mr Trump's comments about barring Muslims from the US were "divisive, unhelpful and wrong".
Education Secretary Justine Greening said Mr Trump's comments about groping women were "utterly crass".
But Mr Trump, who has compared his appeal to the Leave campaign in the UK, could align himself with key Brexiteers.
"There will be some people he would reach out to in the British Cabinet like Liam Fox," Professor Mike Cullinane of Northumbria University has suggested.
"I wouldn't be surprised that he does try and reach out to some of the backbenchers in the Tory party in order to try and build relations."
On trade and any deals that Mr Trump may strike with the UK, Professor Iwan Morgan of University College London warned: "I don't think we could expect any favours when it comes to trade deals.
"Trump will be what you might call a realist. I don't think he has any commitment or feelings for the special relationship."