LONDON, Sept 17, 2025 (BSS/AFP) - US President Donald Trump headed for a historic second UK state visit hosted by his "friend" King Charles III Tuesday -- but political controversies, wars and tariffs threatened to cloud the pomp and pageantry.

Britain is rolling out its royal family in an extraordinary bid to woo the mercurial Trump, with security tight as protesters gear up to make their voices heard against the 79-year-old.

Trump, who has long been fascinated by the British monarchy, is the first US president to be invited for two state visits, after previously being hosted by Queen Elizabeth II during his last term in office in 2019.

King Charles will host Trump at Windsor Castle for a lavish banquet and carriage ride on Wednesday, before Trump meets Prime Minister Keir Starmer at his country residence on Thursday.

"Charles, as you know, who's now king, is my friend," Trump told reporters at the White House before leaving hand-in-hand with First Lady Melania Trump to head to Britain aboard Air Force One.

"He's such an elegant gentleman and he represents the country so well."

Security is tight for the visit and the setting at Windsor Castle means Trump will be far away from crowds, with his schedule due to avoid London, where a large anti-Trump demonstration has been called on Wednesday.

But several dozen demonstrators, holding anti-Trump signs and chanting slogans, rallied on Windsor High Street in the shadow of the castle, late on Tuesday.

A Palestinian flag and a Canadian flag were among the placards held aloft.

- 'Beyond disappointed' -

"I am beyond disappointed," Michelle, 32, head of marketing for an agency who declined to give a surname, told AFP of the UK rolling out the red carpet. She held a "fascists not welcome" sigh. "I am beyond frustrated. I'm beyond upset."

"Donald Trump as a person is I feel like fuelling a lot of the far right protests that we're already having here. It's a humungous problem."

The scale of the British state visit is unprecedented, featuring the first joint flypast by US and UK fighter jets at such an event and the largest guard of honour.

It reflects the British government's desire to use the soft power of the British royals to keep Trump onside, despite his unpredictability over everything from tariffs to Ukraine and Gaza.

The question is whether the bid to dazzle and flatter Trump will work.

Trump indicated that the embattled Starmer will still have his work cut out as Britain seeks to put the finishing touches on a deal to avoid the US president's sweeping global tariffs.

"They want to see if they can refine the trade deal a little bit," Trump said.

Controversies over sex offender Jeffrey Epstein and free-speech culture wars, and Starmer's political troubles at home could also make for some awkward moments.

Trump may however relish a chance to escape a turbulent period at home, where the killing of right-wing activist Charlie Kirk has caused deep turmoil.

The visit is "a huge moment for both" men, said Evie Aspinall, director of the British Foreign Policy Group think-tank.

"For Trump, the state visit is an opportunity to revel in the pomp and ceremony he loves," she told AFP.

"For Starmer, the visit is a chance to distract from domestic discontent and shift the limelight onto international issues where he has had greater success."

- 'Unbreakable friendship' -

Starmer desperately needs the visit to go well following a miserable few days in which some of his own Labour party members have openly questioned whether he can remain as leader.

He has been dogged by questions over his judgement for appointing the now-sacked Peter Mandelson as ambassador to Washington, despite his known friendship with the late Epstein.

Trump is facing awkward scrutiny himself over his own links to the convicted sex offender.

The White House meanwhile said Trump would bring up free speech with Starmer -- a topic raised by Trump's former ally Elon Musk in a televised speech to a far-right rally in Britain over the weekend.

But Downing Street has said Trump's visit would see the "unbreakable friendship" between the countries "reach new heights".

The two nations are set to sign a raft of agreements worth œ10 billion ($13.6 billion) on nuclear and tech projects.

Meanwhile, Melania Trump is also set to cause a stir with her separate itinerary on Thursday -- a rare public appearance for the Slovenian-born first lady.

She is due to take part in an event with Queen Camilla, who is recovering from a bout of acute sinusitis which prevented her from attending the Duchess of Kent's funeral on Tuesday.