US Treasury Secretary Scott Bessent and British finance minister Rachel Reeves led events before Trump's arrival, announcing a "Transatlantic taskforce" to deepen work between two of the world's largest financial centres.
Trump will be greeted by King Charles on Wednesday, UK time, for a day of pomp at Windsor Castle, a regal show of soft power that Starmer hopes will offer him protection from possible pitfalls during the trip.
"My relationship is very good with the UK, and Charles, as you know, who's now King, is my friend," Trump told reporters ahead of landing.
"It's the first time this has ever happened where somebody was honoured twice. So, it's a great honour."
He added: "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, a killing that has appeared to affect the president deeply.
Starmer is also looking to turn the focus onto geopolitics and investment after enduring 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 convicted sex offender Jeffrey 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.
To that end, business executives including Nvidia chief executive Jensen Huang and OpenAI's Sam Altman are due to attend, while billions of dollars of business deals are expected to be announced.
Microsoft said it would invest more than $US30 billion ($A45 billion) in Britain over the next four years, while Google said it would invest STG5 billion ($A10 billion), partly on a new data centre close to London that would help meet demand for AI services.
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 told reporters.
Starmer will turn the focus to foreign affairs on Thursday when he hosts Trump at his Chequers country residence and will attempt to draw a line under his handling of the departures of his deputy, Angela Rayner, and Mandelson.
He gave both his full-throated support before being forced to let them go, prompting questions over his political judgment at a time when Nigel Farage's populist Reform UK party holds a hefty lead in the polls.
On Wednesday, Trump and his wife, Melania, will be treated to British royal pageantry, including a carriage tour, a state banquet, a flypast by military aircraft and a gun salute.
A day later, Starmer welcomes 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.
Both nations will have sizeable delegations and will be largely protected from planned anti-Trump protests.
With PA
