Four people have been arrested after an image of Donald Trump and convicted paedophile Jeffrey Epstein was projected onto the facade of Windsor Castle.

The incident came as the US President and wife Melania arrived in London for his unprecedented second official state visit, where he will later be feted by the King and other members of the royal family.

British police said four adults had been arrested following an “unauthorised projection” at the castle. They described it as a “public stunt”.

“We take any unauthorised activity around Windsor Castle extremely seriously,” Chief Superintendent Felicity Parker said.

“Our officers responded swiftly to stop the projection and four people have been arrested.

“We are conducting a thorough investigation with our partners into the circumstances surrounding this incident and will provide further updates when we are in a position to do so.”

A week ago, Democrats in the US House of Representatives made public a birthday letter Trump allegedly wrote to Epstein more than 20 years ago. The White House has denied its authenticity.

The letter was also projected onto the castle, along with pictures of Epstein’s victims, news clips about the case and police reports.

Political campaign group Led By Donkeys shared an image of the stunt to Instagram with the caption “Hey Donald, welcome to Windsor Castle”.

Earlier, protesters had also unfurled a massive banner near Windsor Castle, featuring a photograph of Trump and Epstein.

Trump was met by Foreign Secretary Yvette Cooper and The Viscount Hood, Lord in Waiting, when Air Force One landed at London’s Stansted Airport late on Tuesday (local time).

(“The ego has landed,” wrote The Mirror newspaper on its live blog of the arrival.)

The Mirror‘s home page as the Trumps arrive in Britain.

Trump gave a thumbs up to waiting media and said he had a “great flight” and was looking forward to a “very good day” tomorrow.

“Well, I love it (Britain). I love Turnberry (his golf course), I love Aberdeen. I have a lot of things here that … they warm my heart. I want to tell you, it’s a very special place,” he said.

He and Melania were expected to stay overnight at Winfield House, the official US ambassador’s residence in London, before being treated to a ceremonial welcome and lavish state banquet at Windsor Castle on Wednesday.

There will also be a carriage tour, a flypast by military aircraft and a gun salute.

Ahead of landing, Trump described the King as “my friend” and said he had a good relationship with Britain.

“It’s the first time this has ever happened where somebody was honoured twice. So, it’s a great honour,” he said of the state visit.

“I’m there also on trade. They want to see if they can refine the trade deal a little bit.

“We’ve made a deal, and it’s a great deal, and I’m into helping them.”

The visit should provide Trump with a diversion less than a week after a close ally, conservative activist Charlie Kirk, was shot dead, sparking further division in the US.

British Prime Minister Keir Starmer is also looking to turn the focus onto geopolitics and investment after a tough couple of weeks that have undermined his authority.

First he was forced to fire his deputy and then six days later his ambassador to the US, Peter Mandelson, over his ties to Epstein.

Starmer wants to pitch Britain as a destination for US investment, closely aligning its financial services, tech and energy sectors with larger American peers to try to drive much-needed economic growth at home.

A spokesperson for Starmer described the state visit as “a historic opportunity” coming “at a crucial time for global stability and security”.

“The Prime Minister will discuss the challenges that both our countries face, and the opportunities, as we enter a new era of our deep and unparalleled relationship,” the spokesperson said.

On Thursday, Starmer will welcome Trump to Chequers, a 16th-century manor house in the southern English countryside, to discuss investment, tariffs on steel and aluminium, ending Russia’s full-scale invasion of Ukraine and the situation in Gaza.

-with AAP