Crowned heads and prime ministers, emperors and presidents from around the world gathered for the Queen’s state funeral, in one of the biggest diplomatic gatherings hosted in the UK in decades.

US President Joe Biden, French President Emmanuel Macron and their controversial Brazilian counterpart Jair Bolsonaro were among the leaders present at the service in London’s historic Westminster Abbey.

Face-to-face mingling continued afterwards at a reception for visiting world leaders at nearby Church House, hosted by Foreign Secretary James Cleverly.

Not everyone made it, with Mr Biden heading from the Abbey straight to the airport and other leaders already on their way to New York for the annual United Nations General Assembly.

But Japan’s Emperor Naruhito and his wife, Empress Masako, on their first visit abroad since he was crowned in 2019, took the opportunity to sign a book of condolence at Church House.

Traditionally, Japanese emperors do not attend funerals due to a cultural belief which considers death to be impure.

At the reception afterwards, the emperor was “quite happy to talk to anybody and everybody and did so with great charm”, a Foreign Office source said.

The presidents of Greece, Namibia, South Korea, the Republic of the Congo were also pictured signing the book, as was Prince Albert of Monaco and European Commission Ursula von der Leyen.

Pakistan’s government tweeted photos of Prime Minister Shehbaz Sharif mingling with Labour leader Sir Keir Starmer, London Mayor Sadiq Khan and former prime ministers Boris Johnson and David Cameron at the event.

Earlier, logistical constraints meant most of the 200 to 250 leaders and their spouses assembled in London had to be bussed in from Royal Hospital Chelsea to prevent a snarl-up of official cars outside Westminster Abbey.

One leader allowed his own transport was Mr Biden, who arrived at the abbey in the armoured presidential limousine, dubbed The Beast, with his wife Jill.

It was caught in traffic on the way, with footage showing it held up outside a Pret a Manger restaurant near Marble Arch in Westminster.

Arriving at the Abbey shortly after 10am, just after the 9.55am deadline Buckingham Palace set for dignitaries to be seated, the Bidens reportedly had to wait briefly at the entrance and follow a procession of George and Victoria Cross-holders down the nave of the abbey before taking their seats.

For other leaders, the shared coaches from west London presented another opportunity for some impromptu diplomacy, after many of those present were at a reception at Buckingham Palace hosted by the King on Sunday.

Canadian Prime Minister Justin Trudeau, attending with fellow Commonwealth premiers Jacinda Ardern of New Zealand and Australia’s Anthony Albanese, said the importance of such informal contacts should not be underestimated.

“Increasingly, in various summits, there is a need to travel on buses and there is actually a lot of work that gets done,” he told the BBC Radio 4 Today programme in an interview ahead of the service.

“This is an opportunity to connect with leaders around the world and carry on some really important conversations, whether it is about the war in Ukraine and Russia’s role in the global food and energy crisis, whether it’s about climate change and the need to do more, whether it’s just standing up for our democracies.

“The reality is in many international summits, the set-pieces and speeches around the table are important but the conversations by the water-cooler, metaphorically, are the important ones.”

Among those crowding onto the coaches were Mr Macron and his wife, Brigitte, and Queen Margrethe II of Denmark, now Europe’s longest-reigning monarch.

European Union president Charles Michel was present, as was Ireland’s President Michael D Higgins and Mr Bolsonaro.

Once inside the abbey, the opportunities for informal diplomatic exchanges may have been more limited with strict protocol dictating the seating arrangements.

Mr Biden and Mr Macron both found themselves perched at the end of a row of seats next to their respective first ladies.

The US President was 14 rows back on the south transept, with Realm governor generals and Commonwealth countries taking precedent in front.

He was behind the Polish leader and in front of the Czech Republic, while the First Lady was next to Switzerland.

Directly across the aisle from Mr Biden’s place, the seat was labelled the Republic of Korea.

Ukraine’s first lady, Olena Zelenska, was four rows behind Mr Macron, representing her war-torn nation on behalf of her husband Volodymyr Zelensky as he continues to organise the fightback against Russian invaders.

China, meanwhile, was represented by vice-president Wang Qishan, despite the objections of MPs who believed that an invitation should not have been extended to Beijing.

King Abdullah II and Queen Rania, of Jordan, King Felipe and Queen Letizia of Spain, and King Carl XVI Gustaf and Queen Silvia of Sweden were among foreign royals to attend.

Saudi Arabia’s Crown Prince Mohammed bin Salman appears to have opted not to attend after activists criticised the decision to invite him.

Invitations were not sent to Russia and Belarus due to the invasion of Ukraine, while Venezuela, Taliban-ruled Afghanistan, Myanmar’s military junta and Syria’s Bashar Assad were also excluded.

North Korea, Nicaragua and Iran were invited only at ambassadorial level.

The Archbishop of Canterbury’s sermon included a line perhaps directed at the world leaders present. He offered a reminder that those who serve will be loved but those “who cling to power and privileges are forgotten”.