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.

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 Washington.

"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. "You can see pressure coming to bear there," said Fraser.

Global economic volatility would hamper Starmer's pledge to fire up Britain's economy so he can invest in the country's flagging health sector, fix prisons, and transition to clean power, among other key objectives.

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, added that 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 a now-deleted LinkedIn post by a Labour official that called for volunteers to travel to North Carolina to campaign 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 in their first face-to-face meeting.

Starmer's official spokesman on Wednesday insisted that the prime minister had developed a good relationship with Trump and that he looks forward to working "closely" with the president-elect.

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 sympathizing sociopath" and a "tyrant in a toupee."

No plan B

Starmer's political spokesperson on Wednesday insisted that Lammy would continue as the UK's top diplomat for the entire five-year parliamentary term.

Another personality clash could come in the shape of Trump supporter and tech billionaire Musk, who sparred with the UK government this summer over far-right riots that swept across England. Ministers rebuked Musk for saying a British "civil war is inevitable."

The UK and US are also likely to disagree on climate, with Trump a self-proclaimed climate change skeptic and Labour determined to make Britain a "clean energy superpower."

Analysts point out that 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 will 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."