London (AFP) -
Grey skies and rain greeted Queen Elizabeth II's coffin as it was brought back to London on a military transport plane on Tuesday, before Britain says a final farewell to its longest-serving monarch.
The giant C-17 Globemaster plane, using the callsign 'Kittyhawk' to signal the queen's presence on board, touched down from Edinburgh at Royal Air Force base Northolt at 6:54 pm (1754 GMT).
The queen's heavy lead-lined oak coffin, draped in the royal standard, was transferred slowly by eight RAF pallbearers into a waiting state hearse for the journey back to Buckingham Palace.
Despite the weather, crowds along the route into central London had built steadily through the day, and outside the palace gates, to catch a glimpse of the coffin.
Queen Elizabeth II died last Thursday aged 96 at her Balmoral retreat in the Scottish Highlands, after almost a year of ill-health that saw her gradually retreat from public view.
Her body was brought first to the monarch's official residence in Scotland, the Palace of Holyroodhouse, in Edinburgh on Sunday, then transferred to St Giles' Cathedral in the city on Monday.
The Scottish government said some 33,000 people filed past her coffin overnight to Tuesday afternoon, before it was taken to the airport.
Accompanying the coffin on the plane, as she did from Balmoral to Edinburgh by road, was her only daughter, Princess Anne, who said it had been 'an honour and privilege' to do so.
'To my mother, The Queen, thank you,' the 72-year-old Princess Royal said in a statement.
Outside St Giles' Cathedral, the Royal Company of Archers, the monarch's bodyguard in Scotland, formed a guard of honour as the coffin emerged to the haunting sound of a lone piper.
At Edinburgh Airport, the Royal Regiment of Scotland, in ceremonial kilts, also formed a guard of honour to the woman dubbed 'Queen of Scots', and the national anthem was played as the plane taxied to the runway.
- Coffin procession -
On Wednesday, the coffin will be moved on a gun carriage at 2:22 pm (1322 GMT) precisely, in a solemn 38-minute procession from Buckingham Palace to Westminster Hall.
She will then lie in state for four full days.
The British government said queues could stretch up to 4.5 miles (7.2-kilometres) alongside the River Thames if the upper end of their estimates is reached.
Some well-wishers began queueing on Monday, sitting on camping chairs and wrapped up in coats and anoraks against the elements or carrying umbrellas.
Others waited to see the casket being driven from RAF Northolt.
'I just want to have a glimpse of the coffin and it's going to be chaos at Westminster,' Joseph Afrane, 59, told AFP as he waited for the hearse to arrive at Buckingham Palace on Tuesday evening.
'Even if it's sad, the atmosphere is actually quite nice here,' he added.
Earlier on Tuesday, the queen's eldest son and successor King Charles III made his maiden visit to Northern Ireland as monarch as part of his tour of all four nations of the United Kingdom.
As heir to the throne, Charles had made 39 visits to Northern Ireland, whose recent history has been scarred by sectarian violence and where a fragile peace has held since 1998.
His 40th visit came as unionists loyal to the crown feel their place in the wider UK is under threat as never before, with Irish nationalists in position to lead the devolved government in Belfast for the first time.
Meanwhile the possibility of a united Ireland is seen as growing.
But at Hillsborough Castle -- the monarch's official residence in Northern Ireland -- King Charles told political leaders that he would work for all communities in the divided province.
'I take up my new duties resolved to seek the welfare of all the inhabitants of Northern Ireland,' he stressed.
Queen Elizabeth's visit to the neighbouring Republic of Ireland in 2011 was the first by a British monarch since its independence from the crown and was seen as a huge step towards cementing the hard-won peace in Northern Ireland.
- 'Behind him' -
Charles and his wife, Queen Consort Camilla, greeted crowds who had turned out early to catch a glimpse of the couple at Hillsborough.
Ceremonial gun salutes in his honour then rang out as the royal standard was raised above the castle southwest of Belfast.
Flowers, cuddly toys and handwritten remembrance notes of the late queen had been left at the gates.
'This is very important for Charles to come here,' Rhonda Irvine, 47, a wedding and events administrator, told AFP.
Describing King Charles's late mother as an 'inspiration for him', she predicted he would be a 'very good' monarch.
Ann Sudlow, 61, a retired nurse from nearby Dromore, had also made the early morning drive 'to show the king that we're behind him as a country and Northern Ireland is supporting him'.
While large crowds welcomed King Charles, visiting the deeply divided region was testing. Nationalist parties boycotted the proclamation of the new king but did meet him.
Belfast's feuding political leaders are split between fiercely loyal British unionists, and Irish nationalists who want to reunify with Ireland. The power-sharing assembly in Belfast is suspended.
King Charles went to an Anglican religious service in the city, also attended by Ireland's President Michael D. Higgins, Prime Minister Micheal Martin and Foreign Minister Simon Coveney.
King Charles shook hands with Higgins, making him the first foreign head of state met by the new British sovereign.
- Crowds -
Britain is in 10 days of national mourning for Queen Elizabeth, who was the constant in national life for seven decades.
King Charles's popularity has recovered since the death of his former wife Diana in a 1997 car crash -- and has surged in recent days, according to a new survey Tuesday.
But he has also been embroiled in several scandals in recent years.
With republican movements gaining ground from Australia to the Bahamas, the new king faces a challenge keeping the Commonwealth realms in the royal fold.
Prime Minister Jacinda Ardern said her country New Zealand, where Charles is also head of state, will likely become a republic in her lifetime.
But she added: 'I don't see it as a short-term measure or anything that is on the agenda soon.'
An unprecedented security operation is being put in place for Monday's state funeral, which is expected to be attended by hundreds of heads of state and government, as well as global royalty.
Neither Russia nor Belarus have been invited, however, following the invasion of Ukraine in February.
'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 television.
Soldiers from the Household Division of regiments, which form the monarch's bodyguard, began practising for the funeral procession in London overnight Monday to Tuesday.
The vast crowds expected in London have resulted in few available hotel rooms, while transport bosses have warned of strong demand.
But not everyone shares the public mood of sadness and remembrance.
British police faced criticism from civil liberties groups on Tuesday over their treatment of anti-monarchy protesters who have publicly challenged King 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'.