Nato marked its 70th birthday by declaring that it was the “most successful alliance in history” and the achievements of the transatlantic partnership deserved to be “fully celebrated”.

But the summit of the group of western nations, supposedly showing its unity and military might, was beset with accusations, recriminations and searching questions about its fundamental aims and values.

The Nato leaders’ meeting – the main event of the three-day summit – due to be held this year in the Grove Hotel in Watford on Wednesday, is normally about setting the policy of the organisation. But this time it has become very much about clashing personalities.

Donald Trump, unsurprisingly, was the loudest voice, calling Emmanuel Macon “nasty” and “very insulting” about the alliance and claiming, without offering any evidence, that France would “break off” from Nato.

Mr Trump was responding to questions about the French president’s own recent highly publicised charge that Nato was “braindead” and Europe should start thinking of itself as a “geopolitical power” to ensure that it remained “in control” of its destiny.

One of the key drivers of Mr Macron’s views was Mr Trump’s repeated criticism of Nato and threats to disengage and cut contributions. The US president announced his arrival at the Nato summit in Brussels last year with insults and threats towards the allies, while praising Russia – a country which allegedly helped put him in the White House – and its leader. Nato, he had previously declared, was “obsolete”.

World news in pictures Show all 50 1 /50 World news in pictures World news in pictures 14 September 2020 Japan's Prime Minister Shinzo Abe, Chief Cabinet Secretary Yoshihide Suga, former Defense Minister Shigeru Ishiba and former Foreign Minister Fumio Kishida celebrate after Suga was elected as new head of the ruling party at the Liberal Democratic Party's leadership election in Tokyo Reuters World news in pictures 13 September 2020 A man stands behind a burning barricade during the fifth straight day of protests against police brutality in Bogota AFP via Getty World news in pictures 12 September 2020 Police officers block and detain protesters during an opposition rally to protest the official presidential election results in Minsk, Belarus. Daily protests calling for the authoritarian president's resignation are now in their second month AP World news in pictures 11 September 2020 Members of 'Omnium Cultural' celebrate the 20th 'Festa per la llibertat' ('Fiesta for the freedom') to mark the Day of Catalonia in Barcelona. Omnion Cultural fights for the independence of Catalonia EPA World news in pictures 10 September 2020 The Moria refugee camp, two days after Greece's biggest migrant camp, was destroyed by fire. Thousands of asylum seekers on the island of Lesbos are now homeless AFP via Getty World news in pictures 9 September 2020 Pope Francis takes off his face mask as he arrives by car to hold a limited public audience at the San Damaso courtyard in The Vatican AFP via Getty World news in pictures 8 September 2020 A home is engulfed in flames during the "Creek Fire" in the Tollhouse area of California AFP via Getty World news in pictures 7 September 2020 A couple take photos along a sea wall of the waves brought by Typhoon Haishen in the eastern port city of Sokcho AFP via Getty World news in pictures 6 September 2020 Novak Djokovic and a tournament official tends to a linesperson who was struck with a ball by Djokovic during his match against Pablo Carreno Busta at the US Open USA Today Sports/Reuters World news in pictures 5 September 2020 Protesters confront police at the Shrine of Remembrance in Melbourne, Australia, during an anti-lockdown rally AFP via Getty World news in pictures 4 September 2020 A woman looks on from a rooftop as rescue workers dig through the rubble of a damaged building in Beirut. A search began for possible survivors after a scanner detected a pulse one month after the mega-blast at the adjacent port AFP via Getty World news in pictures 3 September 2020 A full moon next to the Virgen del Panecillo statue in Quito, Ecuador EPA World news in pictures 2 September 2020 A Palestinian woman reacts as Israeli forces demolish her animal shed near Hebron in the Israeli-occupied West Bank Reuters World news in pictures 1 September 2020 Students protest against presidential elections results in Minsk TUT.BY/AFP via Getty World news in pictures 31 August 2020 The pack rides during the 3rd stage of the Tour de France between Nice and Sisteron AFP via Getty World news in pictures 30 August 2020 Law enforcement officers block a street during a rally of opposition supporters protesting against presidential election results in Minsk, Belarus Reuters World news in pictures 29 August 2020 A woman holding a placard reading "Stop Censorship - Yes to the Freedom of Expression" shouts in a megaphone during a protest against the mandatory wearing of face masks in Paris. Masks, which were already compulsory on public transport, in enclosed public spaces, and outdoors in Paris in certain high-congestion areas around tourist sites, were made mandatory outdoors citywide on August 28 to fight the rising coronavirus infections AFP via Getty World news in pictures 28 August 2020 Japanese Prime Minister Shinzo Abe bows to the national flag at the start of a press conference at the prime minister official residence in Tokyo. Abe announced he will resign over health problems, in a bombshell development that kicks off a leadership contest in the world's third-largest economy AFP via Getty World news in pictures 27 August 2020 Residents take cover behind a tree trunk from rubber bullets fired by South African Police Service (SAPS) in Eldorado Park, near Johannesburg, during a protest by community members after a 16-year old boy was reported dead AFP via Getty World news in pictures 26 August 2020 People scatter rose petals on a statue of Mother Teresa marking her 110th birth anniversary in Ahmedabad AFP via Getty World news in pictures 25 August 2020 An aerial view shows beach-goers standing on salt formations in the Dead Sea near Ein Bokeq, Israel Reuters World news in pictures 24 August 2020 Health workers use a fingertip pulse oximeter and check the body temperature of a fisherwoman inside the Dharavi slum during a door-to-door Covid-19 coronavirus screening in Mumbai AFP via Getty World news in pictures 23 August 2020 People carry an idol of the Hindu god Ganesh, the deity of prosperity, to immerse it off the coast of the Arabian sea during the Ganesh Chaturthi festival in Mumbai, India Reuters World news in pictures 22 August 2020 Firefighters watch as flames from the LNU Lightning Complex fires approach a home in Napa County, California AP World news in pictures 21 August 2020 Members of the Israeli security forces arrest a Palestinian demonstrator during a rally to protest against Israel's plan to annex parts of the occupied West Bank AFP via Getty World news in pictures 20 August 2020 A man pushes his bicycle through a deserted road after prohibitory orders were imposed by district officials for a week to contain the spread of the Covid-19 in Kathmandu AFP via Getty World news in pictures 19 August 2020 A car burns while parked at a residence in Vacaville, California. Dozens of fires are burning out of control throughout Northern California as fire resources are spread thin AFP via Getty World news in pictures 18 August 2020 Students use their mobile phones as flashlights at an anti-government rally at Mahidol University in Nakhon Pathom. Thailand has seen near-daily protests in recent weeks by students demanding the resignation of Prime Minister Prayut Chan-O-Cha AFP via Getty World news in pictures 17 August 2020 Members of the Kayapo tribe block the BR163 highway during a protest outside Novo Progresso in Para state, Brazil. Indigenous protesters blocked a major transamazonian highway to protest against the lack of governmental support during the COVID-19 novel coronavirus pandemic and illegal deforestation in and around their territories AFP via Getty World news in pictures 16 August 2020 Lightning forks over the San Francisco-Oakland Bay Bridge as a storm passes over Oakland AP World news in pictures 15 August 2020 Belarus opposition supporters gather near the Pushkinskaya metro station where Alexander Taraikovsky, a 34-year-old protester died on August 10, during their protest rally in central Minsk AFP via Getty World news in pictures 14 August 2020 AlphaTauri's driver Daniil Kvyat takes part in the second practice session at the Circuit de Catalunya in Montmelo near Barcelona ahead of the Spanish F1 Grand Prix AFP via Getty World news in pictures 13 August 2020 Soldiers of the Brazilian Armed Forces during a disinfection of the Christ The Redeemer statue at the Corcovado mountain prior to the opening of the touristic attraction in Rio AFP via Getty World news in pictures 12 August 2020 Young elephant bulls tussle playfully on World Elephant Day at the Amboseli National Park in Kenya AFP via Getty World news in pictures 11 August 2020 French Prime Minister Jean Castex is helped by a member of staff to put a protective suit on prior to his visit at the CHU hospital in Montpellier AFP via Getty World news in pictures 10 August 2020 Locals harvest their potatoes as Mount Sinabung spews volcanic ash in Karo, North Sumatra province, Indonesia Antara Foto/Reuters World news in pictures 9 August 2020 Doves fly over the Peace Statue at Nagasaki Peace Park during the memorial ceremony held for the 75th anniversary of the atomic bombing EPA World news in pictures 8 August 2020 Anti-government protesters try to remove concrete wall that installed by security forces to prevent protesters reaching the Parliament square, during a protest against the political elites and the government after this week's deadly explosion in Beirut AP World news in pictures 7 August 2020 A protester throws a stone towards Israeli forces in the village of Turmus Aya, north of Ramallah in the occupied West Bank, following a march by Palestinians against the building of Israeli settlements AFP via Getty World news in pictures 6 August 2020 A woman yells as soldiers block a road for French President Emmanuel Macron's visit the Gemmayzeh neighborhood. The area in Beirut suffered extensive damage from the explosion at the seaport AP World news in pictures 5 August 2020 Damage at the site of Tuesday's blast in Beirut's port area, Lebanon Reuters World news in pictures 4 August 2020 A large explosion in the Lebanese capital Beirut. The blast, which rattled entire buildings and broke glass, was felt in several parts of the city AFP via Getty World news in pictures 3 August 2020 A general view shows the new road bridge in Genoa, Italy ahead of its official inauguration, after it was rebuilt following its collapse on August 14, 2018 which killed 43 people Reuters World news in pictures 2 August 2020 Empty stall spaces are seen hours before a citywide curfew is introduced in Melbourne, Australia EPA World news in pictures 1 August 2020 People take part in a demonstration by the initiative "Querdenken-711" with the slogan "the end of the pandemic - the day of freedom" to protest against the current measurements to curb the spread of COVID-19 in Berlin, Germany AFP via Getty World news in pictures 31 July 2020 Pilgrims circumambulating around the Kaaba, the holiest shrine in the Grand mosque in Mecca. Muslim pilgrims converged today on Saudi Arabia's Mount Arafat for the climax of this year's hajj, the smallest in modern times and a sharp contrast to the massive crowds of previous years Saudi Ministry of Media/AFP World news in pictures 30 July 2020 The Mars 2020 Perseverance mission lifts off at the Kennedy Space Centre in Florida. The mission is part of the USA's largest moon to Mars exploration. Nasa will attempt to establish a sustained human presence on and around the moon by 2028 through their Artemis programme EPA World news in pictures 29 July 2020 A woman refreshes herself in a outdoor pool in summer temperatures in Ehingen, Germany dpa via AP World news in pictures 28 July 2020 Malaysia's former prime minister Najib Razak speaks to the media after he was found guilty in his corruption trial in Kuala Lumpur AFP via Getty World news in pictures 27 July 2020 North Korean leader Kim Jong Un poses for a photograph after conferring commemorative pistols to leading commanding officers of the armed forces on the 67th anniversary of the "Day of Victory in the Great Fatherland Liberation War". Which marks the signing of the Korean War armistice KCNA via Reuters

The US president went from Brussels to Britain to meet then-prime minister Theresa May before a summit with Vladimir Putin in Finland. Arriving in Helsinki, he stated: “I have Nato, I have the UK, which is in turmoil and I have Putin. Frankly, Putin may be the easiest of them all. Who would think? Who would think?”

Speaking in London on Tuesday, Mr Trump said: “I am looking at him [Mr Macron] and I’m saying that he needs protection more than anybody and I see him breaking off [from Nato], so I am a little surprised at that.” French diplomats dismissed the US president’s claims of their country leaving Nato as “baseless” and “nonsense”.

Meanwhile claims emerged from Washington that it is America which may leave Nato in the future if Mr Trump wins a second term.

The week this summit began, the US announced that it was cutting its contribution to Nato projects. The sum involved would reduce the funding to the equivalent of Germany’s – a country Mr Trump has castigated for not putting more into the alliance.

John Bolton, the US president’s former national security adviser – his third in three years – suggested in a speech at a private hedge-fund event that Mr Trump could go “full isolationist” and withdraw the US from Nato and other international alliances.

This would be in tune, said Mr Bolton, with a Republican Party being increasingly influenced by the isolationist views of the Tea Party and figures like Senator Rand Paul.

Mr Trump, during the press conference in which he criticised Mr Macron, complained that the “US benefited the least” from Nato. Member states which he thinks are not spending enough on defence will be “dealt with”, he warned, through punitive trade measures, “so they have to pay”.

The television company NBC revealed that in the speech to Morgan Stanley executives, Mr Bolton also claimed that Mr Trump’s approach to Turkey has been motivated by the personal and financial interests of his family.

The Trump organisation has property projects in Istanbul and the US president’s daughter, Ivanka Trump, attended the opening of Trump Towers Istanbul with Recep Tayyip Erdogan in 2012. Mr Trump had himself said in an interview in 2015 that the project could present “a little conflict of interest” should he be elected.

Mr Trump faced widespread criticism in the US, including from Republican members of Congress, and from Nato allies for pulling US troops out of Syria. The decision, taken after a phone call with Turkey’s President Erdogan, left Kurdish YPG forces, which have fought alongside American and other western forces against Isis, to face a Turkish military onslaught.

Threats issued by the Turkish government have become a problem at the Nato summit. Before flying to London Mr Erdogan said he would refuse to approve plans to defend Poland, Lithuania, Latvia and Estonia if Russia attacked unless Nato formally recognised the YPG as a terrorist organisation.

Mr Macron, however, was adamant that “we don’t have the same definition of terrorism around the Nato table”. Last month the French president was the target of Ankara’s wrath for hosting an official from the Kurdish-led Syrian Democratic Forces in Paris.

The Turkish and French presidents were due to meet each other along with German chancellor Angela Merkel and Boris Johnson at Downing Street on Tuesday afternoon.

Jens Stoltenberg, Nato’s secretary general, wanted to reassure members on its eastern flank that they would be defended against any assault by Moscow. “Through the presence of Nato forces in Poland and the Baltic countries, we are sending Russia a very strong signal: if there is an attack on Poland or the Baltic countries, the whole alliance will respond,” he insisted.

Donald Trump says that he doesn't know where the NHS rumour started

How to interact with China will be one of the issues to be discussed by Nato leaders. Mr Stoltenberg said the alliance needed to recognise the challenge posed by Beijing but did not want to make it an enemy.

“What we see is that the rising power of China is shifting the global balance of power, and the economic rise, the military rise, provides some opportunities and also some serious challenges,” he said at the Nato Engages forum in London.

Mr Trump said the US was doing “very well” from the trade war with China and he was in no hurry to sign an agreement before he ran for re-election next November. The FTSE 100 dropped more than 100 points in reaction, and the US stock markets were also expected to open lower.

The US has also threatened to slap 100 per cent tariffs on French products including cheese and champagne in retaliation for a French tax on global tech corporations Google, Amazon and Facebook.

Mr Macron said: “We’ll see where the discussions lead in the coming weeks, but it will involve a European response because, in effect, it wouldn’t be France that is being sanctioned or attacked but Europe.

“My first question is what will happen with the United Kingdom, which adopted the same tax? For Italy, the same tax? Austria, Spain. If we’re serious, those countries will have to be treated the same way.”