US president Donald Trump arrived in London on Monday night for a Nato summit, amid concerns about his country’s commitment to the defence alliance that is marking its 70th anniversary.

Speaking as he left Washington with his wife, Melania, Mr Trump reiterated his complaints that the US is contributing too much in defence spending compared with its fellow Nato members.

“It has not been a fair situation for us because we pay far too much, as you know,” he said, describing other members as “delinquent”.

This week’s leaders’ meeting, which opens on Tuesday, comes at a challenging time in the history of the transatlantic alliance, which was founded in the years following the second World War as a bulwark against Soviet aggression.

Mr Trump has long criticised the international body, previously describing Nato as “obsolete”.

While his calls for European members to contribute more echoes the sentiment of previous presidents, including Barack Obama, his suspicion of multilateral organisations such as Nato is unprecedented for a US commander-in-chief.

Mr Trump has been a disruptive presence at previous Nato meetings. In Brussels in June 2018, the US president threatened to pull the US out of the alliance unless Europe paid more, singling out Germany in particular for criticism.

Mr Trump’s unpredictable behaviour is perhaps one reason why this week’s meeting is shorter than usual, centred around a dinner at Buckingham Palace on Tuesday evening, followed by the main session at the Grove hotel in Watford on Wednesday.

In an effort to appease the US president, Nato members are expected to confirm a reduction in the US’s contribution to the organisation’s $2.5 billion operating budget – the cost of running Nato’s headquarters, staff and other expenses – with some European members, Canada and Turkey paying more, despite objections from France. As a result, the US contribution will fall to 16 per cent, in line with Germany.

Nonetheless, the question of how much Nato members spend on their military is likely to preoccupy minds.

Only a handful of the 29 members meet or exceed the target of spending two per cent of GDP (gross domestic product) on defence.

On Friday, Nato secretary general Jen Stoltenberg announced that European members and Canada had increased their defence spending by 4.6 per cent in real terms in 2019. “This is unprecedented progress and it is making Nato stronger,” he said.

‘Tremendous progress’

The White House has already seized on indications that allies are upping their contributions, suggesting that it is a result of Mr Trump’s efforts.

Speaking to reporters ahead of Mr Trump’s departure for London, a senior White House official noted that allies have added more than $100 billion in new spending since Mr Trump has taken office. “This is tremendous progress, and I think it is due to the president’s diplomatic work,” he said.

Mr Trump picked up on this point as he departed the White House on Monday, saying that Mr Stoltenberg had told him he was responsible for securing the extra funding “from other countries that we protect – they weren’t paying”.

Mr Trump has a series of bilateral meetings on his agenda, including one-to-ones with German chancellor Angela Merkel, French president Emanuel Macron and Mr Stoltenberg.

With Britain due to go to the polls next week in a general election, no bilateral meeting has been scheduled between Mr Trump and British prime minister Boris Johnson. However, the two men spoke by phone on Saturday following the terrorist attack in London, with the White House saying that they “look forward to meeting with one another” at the Nato leaders’ meeting.

While Mr Trump is a strong supporter of his British counterpart, Mr Johnson tactfully said in an interview that it would be “best” if Mr Trump did not get involved in Britain’s general election.