Heraldo de Madrid - Royals escort queen on final journey from Buckingham Palace

The king, his siblings, and sons, princes William and Harry, walked at 75 steps a minute behind the horse-drawn gun carriage carrying the queen's body to Westminster Hall, where hundreds of thousands of people will pay their last respects.

Soldiers in red dress uniform played Beethoven's Funeral March and Big Ben tolled out each minute as the casket -- covered by a royal standard and topped with the Imperial State Crown -- passed in front of hushed crowds lining the route.

The grand procession through the flag-lined heart of London represented the latest spectacular step in the 11 days of intricately choreographed national mourning across the United Kingdom that will culminate with the funeral on Monday of its longest-reigning monarch.

The sight of the new king's two sons inevitably evoked memories of 1997, when William and Harry, then aged just 15 and 12, walked, heads bowed, behind the coffin of their mother, princess Diana.

But it comes with the once-close brothers now reportedly not on speaking terms, after Harry's move to the United States.

The public, some of whom began queueing on Monday, will begin filing past the coffin from 5:00 pm (1600 GMT), with mourners already warned they will face an endurance test to wait in lines that could tail back five miles (eight kilometres).

Hundreds of people were already queueing at around 8:20 am with those at the front having spent the night equipped with blankets, camping seats, a tents and rain ponchos.

As day broke, a steady stream of mourners joined the back of the queue along the River Thames under the watchful eye of an army of stewards in fluorescent jackets.

"The night was quite wet, cold and wet, but I got a little chair and a big umbrella so I kept fairly dry," Dan Ford, a 52-year-old retired police officer, told AFP.

Brian Flatman, 85, said there was "no way" he would pass up the chance to pay his respects having missed the queen's 1953 coronation.

"I was 16, we got there before midnight, Hyde Park Corner, superb position, but very quickly I became suddenly ill and had to crawl all the way to South London," he recalled.

"This time there is no way I can miss that. I will dedicate a few seconds there (by the coffin) to her life of dedication. What an example."

Strict rules and airport-style security measures have been put in place, with "far more" people expected than the 200,000 who filed past the coffin of the queen's mother when she died in 2002, according to Prime Minister Liz Truss's spokesman.

The government has advised people to wear "suitable clothing" and to bring portable battery packs to keep their mobile phones charged -- an indication that some people will need to wait overnight for a glimpse of the casket.

Hotel rooms in the British capital are increasingly hard to find, with even budget rooms going for £300 ($350) per night, while transport bosses and police are under pressure to keep the city moving and safe in exceptional circumstances.

"It's a massive challenge for the Metropolitan Police and for me personally, but we have been preparing for many, many years," the newly appointed head of the London police force, Mark Rowley, told Sky News on Tuesday.

- UK tour -

The body of the late 96-year-old queen, who died "peacefully" at her Balmoral estate in Scotland on Thursday, was flown to London aboard an RAF plane on Tuesday evening from the Scottish capital Edinburgh.

It was then driven to Buckingham Palace, past crowds of motorists who stopped their vehicles at the side of the road to catch a glimpse of the coffin.

Her arrival was greeted with the flashes of thousands of mobile phone camera lights, under the illuminated columns of the landmark palace.

"Welcome Home Ma'am," The Sun tabloid said on Wednesday on its front page. The Times ran with the headline "Home to Rest" and the Daily Mail "Home to her Family".

The procession on Wednesday mirrored a similar ceremony in Edinburgh on Monday when her coffin was driven through the hushed streets of the city to lie "at rest" at St Giles' Cathedral.

There, some 33,000 people filed past the coffin overnight to Tuesday afternoon, the Scottish government said.

"Scotland has now bid our Queen of Scots a sad, but fond farewell. We will not see her like again," said First Minister Nicola Sturgeon.

After Scotland and England, Charles continued his tour of the four nations of the United Kingdom on Tuesday by visiting Northern Ireland for the first time as king. He visits Wales on Friday.

The 73-year-old new head of state has won wide praise in the British media for his dignified and often heartfelt reaction to his mother's death, which has led to a rare moment of public unity in Britain.

He has seen his popularity recover since the death of his former wife Diana in a 1997 car crash -- and his ratings have surged in recent days, according to a new survey on Tuesday.

The mourning has also obscured -- albeit briefly -- the broader country's sharp political divisions and a severe cost-of-living crisis that is expected to cause a major increase in poverty over the winter.

- No invite for Putin -

The procession on Wednesday meant another prominent role for the queen's scandal-hit son Andrew, who settled a case in the US earlier this year in which he was accused of sexually assaulting a 17-year-old.

Not everyone shares the public mood of sadness and remembrance sparked by the queen's death, with royal fatigue increasingly evident on social media in the face of blanket media coverage.

British police have also faced criticism from civil liberties groups over their treatment of anti-monarchy protesters who have publicly challenged Charles' accession to the throne.

Video footage and witnesses have drawn attention to police arresting or intimidating people who shouted slogans against the monarchy or held up placards reading "Not My King".

The queen's funeral will take place in Westminster Abbey in front of 2,000 VIP guests, with the day declared a public holiday in Britain.

US President Joe Biden has confirmed he will attend, as will French President Emmanuel Macron and Canadian Prime Minister Justin Trudeau.

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Z.Quintana--HdM