Crowned heads and prime ministers, emperors and presidents from around the world were gathered for the state funeral of the Queen.

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

It was 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 French President Emmanuel 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 Brazil’s controversial President Jair Bolsonaro.

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

Once inside, 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.

Other notable attendees were Japan’s Emperor Naruhito and his wife, Empress Masako, making their first visit abroad since he was crowned in 2019.

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

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.