The alliance’s 70th anniversary will be marked at the high-profile summit in the British capital.

NATO leaders are convening in a northwest London suburb better known for its struggling football club than its hosting of international summits of the world’s leaders.

As US President Donald Trump flew across the Atlantic – just 10 days before a crucial general election in the United Kingdom – he boasted he had convinced European allies to boost defence spending, tweeting: “Since I took office, the number of NATO allies fulfilling their obligations more than DOUBLED.”

Fellow NATO leaders attending the summit in Watford will be relieved that Trump, who derailed last year’s agenda with his demands, appears to be satisfied with how the allies have stepped up their military investment.

But UK Prime Minister Boris Johnson will still be nervous that Trump’s presence will hurt him in the closing stages of the British election campaign.

The Brexit-pushing premier is the favourite in the opinion polls before next week’s vote, but opposition Labour leader Jeremy Corbyn has attacked him for his closeness to Trump.

In particular, Labour campaigners have warned that Johnson is ready to grant US drug firms more profitable access to the UK National Health Service in exchange for a US trade deal. Johnson denies this.

Trump has previously urged the prime minister to form an alliance with populist right-winger and Brexit Party leader Nigel Farage – while warning that Corbyn would take the UK to “bad places”.

Johnson said last week that “close friends and allies” such as the UK and the US should not get involved in each other’s elections.

The US leader will hold a number of bilateral meetings alongside the main summit over two days, and will dine with Queen Elizabeth at Buckingham Palace on Tuesday.

The prime minister will break off from campaigning to host the gathering marking NATO’s 70th anniversary.

The talks take place amid a bitter dispute between French President Emmanuel Macron and Turkish President Recep Tayyip Erdogan over Turkey’s recent operation in northern Syria.

Macron infuriated Ankara when he suggested NATO was suffering from “brain death” over the lack of coordination after Turkey’s “crazy” attack on the Kurds, seen as a key Western ally in the fight against the ISIL (ISIS) group.

The Turkish president, who has long sought a free hand against the Kurds, hit back, accusing Macron of “a sick and shallow understanding” of terrorism, suggesting he was the one who was “brain dead”.

Johnson is expected to try to play peacemaker on Tuesday when he hosts the two leaders, together with German Chancellor Angela Merkel, for talks in his official residence before the main gathering.

The prime minister’s official spokesman said: “The PM’s position is that NATO is the most enduring and successful alliance in military history and that it continues to adapt to the evolving threats that we face.

“It is the cornerstone of Euro-Atlantic security and it helps to keep a billion people safe.

“The PM will emphasise that all members must be united behind shared priorities so NATO can adapt to the challenges ahead.”