Promoters of Britain’s divorce from the EU had said they would revitalise bonds with the US, where President Donald Trump, with his shared disdain for multinational bodies, seemed the perfect partner.

Come January, Britain both definitively leaves the 27-nation bloc and will deal with a new US president, Joe Biden, who prioritises the EU and shares none of the Brexiteers’ romanticism about going it alone.

Biden, an Irish-American who will be the second Catholic president, had already warned Prime Minister Boris Johnson not to jeopardise peace in Northern Ireland by erecting a hard border between the British-ruled province and EU member Ireland.

Even as trade talks dragged on, Britain reached a deal with Brussels on special arrangements for Northern Ireland – a sign to observers that Biden’s election had already made an impact.

Jacob Kirkegaard, a senior fellow at the German Marshall Fund of the US, said: “It was recognised in London that if you messed up the Northern Irish border, it would have been absolutely poisonous for the US-UK relationship.”

Johnson’s Conservative government has emphasised issues on which it enjoys common ground with Biden, including fighting climate change, and announced a historic boost in military spending.

Kirkegaard said Britain was hoping to punch above its weight as a strategic security partner of the US, especially at a time of high tension with China, but said Biden could find similar capabilities in the much larger EU, where France is a major military player.

He said: “Brexit Britain has made itself nice to have but no longer strictly necessary to have onboard for the US.”

Biden is surrounded by Barack Obama’s former aides who have not forgotten Johnson’s 2016 quip, in line with thinking on the US far-right, that the then-US president had an “ancestral dislike” of Britain because of his “part-Kenyan” heritage.

While the racial undertones differ markedly, Biden has himself said, at least partly in jest, that his Irish ancestry soured him on Britain.

In footage that went viral after his election, Biden is seen walking on as a BBC journalist tries to ask him a question, responding, “The BBC? I’m Irish!” before flashing a friendly smile.

“Clearly I think there is a sense among some people in Biden’s orbit that Brexit was a completely misguided policy and Prime Minister Johnson has been too close to Trump and therefore there’s a need to downplay this relationship a little bit,” said Erik Brattberg, director of the Europe programme at the Carnegie Endowment for International Peace.

But he said that Biden recognises the broader importance of ties with Britain and would not be a flip image of Trump, who shattered diplomatic protocol by belittling allied leaders, especially German Chancellor Angela Merkel.

He said: “Trump’s approach was more about fomenting divisions within Europe, whereas Biden will see his legacy as trying to heal some of the divisions.”