Queen Elizabeth II dies — follow the latest news as the world mourns
Many have been asked to share buses from an undisclosed location in west London to avoid the traffic around Westminster Abbey grinding to a halt.
But Whitehall sources said Mr Biden, who has confirmed his attendance, would be allowed to travel to the abbey in his armoured Cadillac, known as The Beast, for security reasons.
One government source said it clearly would not be appropriate to ask G7 leaders to “take a bus”, but dignitaries were being asked to be as flexible as possible.
With officials facing the largest gathering of foreign dignitaries in England since Sir Winston Churchill's funeral in 1965, an unprecedented logistical and diplomatic operation is under way to prepare for the arrival of leaders from around the world.
Rehearsals for procession of Queen Elizabeth's coffin in London - in pictures
“This is the biggest international event we have hosted in decades,” a Whitehall source said.
The source compared the logistical task to organising “hundreds of state visits” within a matter of days. Normally, there might only be two or three a year.
It presents a huge logistical, diplomatic and security challenge, with practice runs taking place in the dead of night.
Invitations were sent over the weekend to the heads of state of nations with which the UK has diplomatic relations. For most countries, that means the head of state plus one guest.
An official list has not yet been published, but the event will see about 500 dignitaries from around the world descend on London to pay their last respects to the long-reigning monarch.
The UK mourns Queen Elizabeth II - in pictures
The leaders of most Commonwealth countries are expected to attend, with New Zealand Prime Minister Jacinda Ardern saying she will make the nearly 24-hour journey with a delegation of five others.
Canadian and Australian prime ministers, Justin Trudeau and Anthony Albanese, have also confirmed they will be attending.
Mr Albanese said he would not be travelling alone, tweeting that at Buckingham Palace’s invitation, he and Governor General David Hurley will be accompanied by “10 Australians who have made extraordinary contributions".
Mr Macron, Germany’s Frank-Walter Steinmeier, Italy’s Sergio Mattarella, Turkey’s Recep Tayyip Erdogan and Brazil’s Jair Bolsonaro are among the presidents attending, along with the European Commission’s Ursula von der Leyen.
King Felipe of Spain and his wife, Queen Letizia, are among the European royals who will attend.
Emperor Naruhito of Japan is also expected to travel to London in what would be his first overseas trip since ascending the throne in 2019.
Queen Elizabeth II's coffin arrives at Buckingham Palace - video
The guest list for the Duke of Edinburgh’s memorial service could provide an idea of who else might come.
The 1,800-strong congregation featured about 30 foreign royals, including Prince Albert of Monaco, Denmark’s Queen Margrethe, and King Harald and Queen Sonja of Norway.
But it is not thought the trip will be made by Ukrainian President Volodymyr Zelenskyy, who took time out from organising his country’s fightback against Russian President Vladimir Putin’s forces to sign a book of condolence for the queen.
Arrival times will vary from leader to leader, Downing Street said.
British Prime Minister Liz Truss is not expected to hold any “formal” bilateral meetings with world leaders during the mourning period, but “there may be informal conversations that take place”, her spokesman said.
Former Conservative leader Lord Hague said that while there would “of course” be diplomacy surrounding the funeral, that was not the main focus.
“Of course there is some diplomacy – you can’t have that number of people together from around the world without them starting to say, ‘Well, what do you think is happening in Ukraine?’” he told Times Radio.
“Nevertheless, they’re coming because they want to pay their respects to this extraordinary head of state. And that is what 90 per cent of it will be about.”
RAF plane carrying Queen Elizabeth II's coffin lands in London - video
Downing Street on Monday refused to comment on reports that world leaders visiting London for the queen’s funeral have been asked to travel on commercial flights and will be bused to Westminster Abbey.
“Arrangements for leaders, including how they travel, will vary depending on individual circumstances,” the spokesman said. He said “the guidance and information provided is guidance”.
Leaders are expected to begin arriving in Britain from Friday and time has been set aside on Sunday for them to pay their respects to the queen as she lies in state in Westminster Hall.
On Sunday evening they will attend a reception at Buckingham Palace hosted by King Charles III.
Leaders will be able to sign an official condolence book at Lancaster House.
Queen Elizabeth II's lying in state explained - video
They will also be invited to deliver a tribute to the late queen lasting up to three minutes, which will be recorded for the media.
There will be two receptions for dignitaries after the service.
Members of the royal family will attend the first event at Windsor Castle after the procession of the queen from Westminster Abbey to St George’s chapel at Windsor.
A second-tier event will take place in Church House for other leaders, which will also include senior government ministers and diplomats.