President Donald Trump and First Lady Melania Trump depart the UK on board Air Force One - here's a look back at the two-day state visit
In a joint press conference earlier, Trump suggested Keir Starmer could involve the military in tackling the UK's small boat crisis
Trump also said Vladimir Putin "let me down", as Starmer said both countries are working to put pressure on the Russian president to agree to a Ukraine peace deal
When asked about Starmer's plan to recognise a Palestinian state, Trump said he has "a disagreement with the prime minister on that score"
Some of the thorniest issues did not really crop up. Jeffrey Epstein and Lord Mandelson only perfunctorily, and Nigel Farage not at all, writes chief political correspondent Henry Zeffman
It comes after the leaders signed a new "technology prosperity deal" with firms including Microsoft and Google pledging to spend billions in the UK
Air Force One is touching down at London Stansted Airport with President Donald Trump and First Lady Melania Trump on board.
Stay with us - we'll have the latest with you as we get it.
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Image source, BBC POOLAir Force One is set to touch down at London Stansted Airport any moment now.
We're seeing images of reporters and cameramen gathering on the tarmac, all awaiting Trump's arrival.
Image source, PA MediaThe moment Starmer gave Trump the invite from King Charles III
President Trump’s positive words about his second UK state visit began immediately after he was handed the invitation by Sir Keir Starmer.
In February:
As he was given the invite in the White House's Oval Office, Trump told Prime Minister Starmer that it was a "great, great honour" to receive the King's letter. "That says at Windsor; that's really something," he added.
"We look forward to being there and honouring the King and honouring, really, your country," he told the PM.
In April:
Trump told reporters: "They're going to do a second, as you know, a second fest… that's what it is: a fest, and it's beautiful, and it's the first time it's ever happened to one person.
Image source, Getty ImagesTrump meeting his "friend" King Charles during his first state visit to the UK in 2019
"I'm a friend of Charles, I have great respect for King Charles and the family, William. We have really just a great respect for the family," he added.
In July:
Asked in the summer what he hopes to achieve during his visit, Trump told the BBC: "I think I want to have a good time and respect King Charles because he's a great gentleman."
Trump also praised Starmer, who he said he "really likes" even though "he's a liberal".
Before boarding Air Force One today:
As we reported earlier, before boarding his presidential jet President Trump called the King "my friend" and described him as "such an elegant gentleman... he represents the country so well".
Image source, ReutersPolice officers conduct security searches in Windsor ahead of President Trump's arrival
The biggest protective security operation since the Coronation is now in place for President Trump’s visit.
Police boats line the Thames, with snipers and drones also in place.
The recent murder of far-right activist Charlie Kirk in the United States, as well as last year's assassination attempt on Trump, means that security is tighter than ever.
There will be no public-facing engagements for the duration of the president's two-day visit.
On Wednesday, Trump is expected to be with the King in Windsor before heading to Chequers - Prime Minister Sir Keir Starmer's country residence - on Thursday.
Meanwhile, Thames Valley Police on Tuesday have said they arrested two men for allegedly flying drones that breached air space restrictions in place for Trump's visit.
Image source, ReutersDozens of people have been gathering in Windsor to protest against US President Donald Trump's state visit.
The group of protestors has been chanting: "Say it loud, say it clear, Donald Trump's not welcome here."
Further protests are also expected tomorrow, with the Stop Trump Coalition, which comprises 50 unions and charities, saying they will stage a national demonstration in London against the state visit.
Meanwhile, Republicans Overseas UK are holding a reception and dinner at Windsor Guildhall this evening.
Image source, BBC POOLThe helicopter that will pick up President Trump and his wife Melania once they land has just arrived at London Stansted Airport.
We're expecting Air Force One to land shortly - we'll bring you an update on this when we have it.
"They're politically different, they're personally incredibly different. I find it difficult to imagine what small talk they make between themselves, the BBC's North America Editor Sarah Smith says.
"However, "they do spend a lot of time together and it seems to work", she adds.
In this short two-minute video, the BBC's Political Editor Chris Mason and Sarah Smith analyse what's at stake for both sides during the US president's second UK state visit:
Image source, PA MediaPolice officers on patrol outside Windsor Castle
Preparations have been under way in Windsor for US President Donald Trump's state visit.
Tomorrow, King Charles is set to host the president and First Lady Melania Trump at Windsor Castle for the first of two days of events
Here are some of the pictures we've been seeing from the town.
Image source, ReutersMilitary personnel have been taking part in rehearsals ahead of the visit
Image source, Reuters'Bobble head' souvenirs of Trump and the King on display at a shop
Simon Jack
Business editor
Image source, Getty ImagesA proposed deal to eliminate tariffs on UK steel exports to the US has been put on hold indefinitely, the BBC understands.
Tariffs of 25% are currently applied to steel exports to the US, which make up 6% of all UK steel exports by volume and 9% by value. Other countries face tariffs of 50% and so senior government sources insist that the UK is in a competitive position relative to others.
This comes as President Donald Trump hailed the "great honour" of being hosted by King Charles at "the ultimate" Windsor Castle for his second state visit, and hinted at possible tariff relief for UK steel.
The UK and US signed a trade deal in June that reduced tariffs on car and aerospace imports to the US, but failed to agree on terms for British steel, leaving tariffs on it at 25%.
Speaking to reporters as he boarded Air Force One, Trump said he is "into helping" Britain on fine-tuning the UK-US trade deal.
"They want to see if they can refine the trade deal a little bit."
Trump and Melania's state visit to the UK will see them joined by various US officials. Secretary of State Marco Rubio is one of them and we reported a short while ago that he has already landed.
Others expected to join the cohort include the US Treasury Secretary Scott Bessent, Commerce Secretary Howard Lutnick, Agriculture Secretary Brooke Rollins, Trump's special envoy Steve Witkoff and chief of staff Susie Wiles.
Secret service personnel and White House aides are also among staff who typically join trips such as this.
Trump will arrive in the UK on his customised, high-spec Boeing 747-200B aeroplane known as Air Force One.
Image source, Getty ImagesAbout four hours ago, President Trump and his wife Melania took off on Air Force One and started their journey across the Atlantic.
They're expected to touch down later this evening at London Stansted Airport for the president's second state visit to the UK.
Here's the moment the couple were seen boarding the presidential jet in the United States earlier:
Image source, Getty Images
Where will it take place?
US President Donald Trump and his wife First Lady Melania Trump will be hosted at Windsor Castle.
The location was chosen as the typical venue, Buckingham Palace, is currently undergoing renovations.
Like all visits of this kind, the event will include a full ceremonial welcome and a state banquet in St George's Hall, Windsor Castle.
Who will be involved?
All senior members of the Royal Family will be involved, including the Prince of Wales and Catherine, Princess of Wales.
Will Trump be seen in public?
Any visit from a US president brings with it security challenges, and Trump's programme is unlikely to include public-facing events.
During his 2019 visit, there was no procession along The Mall for security reasons and Trump was mostly flown between locations instead of travelling by road.
We don't yet know whether Trump will speak to parliamentarians, which is often included in the choreography of a state visit.
Image source, ReutersUS Secretary of State Marco Rubio has just landed at London Stansted Airport, ahead of Donald Trump who's expected to land on Air Force One later this evening.
He has been greeted by UK Foreign Secretary Yvette Cooper.
James Landale
Diplomatic correspondent
Image source, Getty ImagesThis state visit is designed to improve UK-US relations and cement the government’s relationship with an at-times-unreliable ally.
Diplomats say the president will focus on royal pageantry and avoid controversy.
But the potential for disagreement remains.
Peter Mandelson: The sacking of Lord Mandelson as the UK’s man in Washington, for his links to the convicted paedophile Jeffrey Epstein, will cast a pall.
Questions about this may dominate Thursday’s news conference.
The risk for ministers is that the focus shifts from Prime Minister Starmer’s competence to President Trump’s links to Epstein.
Middle East: The UK is expected to recognise Palestinian statehood at the United Nations next week to keep alive the idea of a two-state solution.
The US is fiercely opposed to this, saying the move would reward terrorism and encourage Israel to annex parts of the West Bank.
Free speech: The White House claims UK regulation of the Internet threatens free speech, which is something ministers reject.
US officials say the issue may come up, as it is something “we in this administration are very much focused on”.
Protests: This state visit will take place behind a ring of steel away from the public.
But anti-Trump demonstrations are planned and the president could push back angrily if he watches coverage of the protests on television.
Image source, Getty ImagesThe late Queen Elizabeth II and Prince Philip pose with President Barack Obama and his wife, Michelle, ahead of a state banquet at Buckingham Palace in 2011
It's a formal trip to the UK by a head of state and is normally at the invitation of the King, who acts on advice from the government.
Although they're grand occasions, they're not just ceremonial affairs - they're also used by the government to further what it sees as Britain's national interests.
Trump is only the third US president to make a state visit to the UK, after George W Bush in 2003 and Barack Obama in 2011.
Just before President Trump boarded Air Force One and departed the US a few hours ago, he spoke about his relationship with King Charles III, who he calls "my friend".
The US president says the King is "such an elegant gentleman" and adds that he "represents the country so well".
You can see Trump's comments in this short video clip:
Jack Burgess
Live page editor
Image source, PA MediaDonald Trump and his wife Melania alongside King Charles III and Queen Camilla, who were then the Prince of Wales and Duchess of Cornwall, during the US president's first state visit in 2019
President Trump's unprecedented second state visit to the UK is about to get under way.
Since the start of Queen Elizabeth II's reign in 1952, there have only been three state visits by US presidents - George W Bush in 2003, Barack Obama in 2009 and Donald Trump in 2019.
From carriage processions through the grounds of Windsor Castle to a State Banquet in St George's Hall, over the next two days the red carpet will be rolled out for President Trump on his second state visit.
It's a significant moment and careful preparation for the visit has been going on for months.
It will give Prime Minister Starmer's government a significant opportunity to build on US-UK relations.
However, the visit is not without its potential pitfalls, as the BBC's diplomatic correspondent James Landale writes.
We'll be bringing you all the latest updates and analysis right here on this page over the next couple of days.