Keir Starmer has insisted that the UK-US special relationship will "prosper" under Donald Trump but the British prime minister's Labour government has multiple reasons to fear the Republican's presidential comeback.
Possible trade wars, Labour ministers' unflattering comments about Trump, and any role for Starmer critic Elon Musk in Trump's administration would make for a bumpy ride between the allies.
The UK's "iron-clad" support for Ukraine in its war against Russia's invasion and "unwavering commitment" to the NATO military alliance are also likely to become major bones of contention, experts said.
Starmer made a first move late on Wednesday, phoning Trump to offer his congratulations, telling reporters at a European summit in Budapest Thursday that the call was "very positive, very constructive".
But Richard Whitman, an international relations professor at the University of Kent, said the centre-left government in London will be feeling "nervous" about Trump's return to the White House.
"Most of the broad parameters of British foreign policy are set by responding to what are the major preoccupations of the United States," he told AFP, noting doubts over Trump's commitment to Ukraine and NATO.
Britain has been one of Ukraine's biggest financial and military backers since Russia's full-scale invasion in February 2022 and any shift in policy by Trump would leave the country in an unenviable position.
"(The UK) can't do a 180-degree shift on Ukraine because it's invested too much," said Whitman.
Simon Fraser, formerly the top civil servant in the UK's foreign ministry, added that the UK-US relationship could be complicated by Trump's approach to the European Union -- and whether that includes tariffs on allies.
Trump has threatened to impose tariffs of up to 20 percent on all US imports and 60 percent on Chinese goods.
Economic unpredictability
A trade war between Trump and the EU could see the UK stuck in the middle.
Global economic volatility would hamper Starmer's pledge to fire up Britain's flagging economy.
The National Institute of Economic and Social Research, a leading think tank, has warned that Trump's tariff plans could halve UK economic growth in the next two years, pushing up prices and interest rates.
Lindsay James, investment strategist at Quilter Investors, said a Trump presidency makes it "unlikely that any (UK-US) trade deal negotiations will be resurrected".
"The UK holds no obvious bargaining chip," she added.
Labour is historically close to the Democratic Party, and several senior figures attended its convention in Chicago in July when Kamala Harris was anointed its presidential candidate.
Last month, Trump accused Starmer's government of "blatant foreign interference" in the US election over the visit and Labour staffers campaigning for Harris.
Behind the scenes, Labour has spent recent months trying to build bridges with Trump's team, and Starmer dined for two hours with Trump in September.
Previous comments by senior Labour figures have the potential to make dealings awkward, however, none more so than for Foreign Secretary David Lammy, who in 2018 called Trump a "woman-hating, neo-Nazi sympathising sociopath" and a "tyrant in a toupee".
Senior minister Pat McFadden on Thursday said Trump was a "fan of the United Kingdom" and Starmer's face-to-face meeting with him had been "productive".
"I think in the end, those shared values and interests are more important than some tweet from however many years ago," he said. "You can move past these things."
No plan B
Starmer's political spokesperson on Wednesday insisted Lammy would stay in his post for the entire five-year parliamentary term.
But trouble could also come from Trump supporter and tech billionaire Musk, who earned a rebuke from ministers this summer after claiming that far-right riots across England would lead to "civil war".
Britain and the United States are also likely to disagree on climate, with Trump a self-proclaimed climate change sceptic and Labour determined to make Britain a "clean energy superpower".
Analysts point out the special relationship, forged during World War II, has endured for 80 years despite multiple governments of different persuasions on both sides of the Atlantic.
"Political differences at the top don't mean that the whole relationship is vulnerable. There are checks and balances," said Fraser, citing "institutional structures".
Whitman agreed that it would endure but added: "If it doesn't, then a great thick pillar of British foreign and security policy crumbles.
"And if you set that against what's already happened with (leaving) the EU, (then) the UK is really adrift.
"The UK doesn't have a hedging strategy. It doesn't have a plan B for its relationship with the US."
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
