King Charles III entered London’s Westminster Abbey on Saturday for a solemn Christian coronation steeped in 1,000 years of history and tradition, but adapted to reflect 21st-century Britain.

The build-up to the ceremony — the religious confirmation of Charles’s accession after the death of his mother Queen Elizabeth II last September — has been mostly celebratory.

But even before Charles, 74, and Queen Camilla, 75, left Buckingham Palace aboard the Diamond Jubilee State Coach for a rainy procession to the abbey, police arrested dozens of protesters using new powers rushed onto the statute book to crack down on direct action groups.

The anti-monarchy movement Republic — which wants an elected head of state — said six of its organisers were detained, while climate activists Just Stop Oil said 19 of its number were held.

Nevertheless, dozens of Republic activists held aloft banners on the route of the procession route, declaring: ‘Not My King.’

Both Human Rights Watch and Amnesty International voiced concern at the arrests.

‘This is something you would expect to see in Moscow, not London,’ HRW said.

London’s metropolitan police has some 11,500 officers on the streets in one of its biggest ever security operations. It has warned that it has an ‘extremely low threshold’ for protests.

The coronation is the first since 1953 and the first of a king since 1937. It is only the second to be televised and the first in colour and streamed online.

It will see the St Edward’s Crown — a solid gold, sacred symbol of the monarch’s authority used only once in the reign — placed on Charles’s head at 1100 GMT to cries of ‘God Save the King’.

Trumpet fanfares will sound through Westminster Abbey and ceremonial gun salutes will blast out across land and sea to mark the first coronation of a British monarch since 1953 — and only the fifth since 1838.

Bells will peal in celebration at churches across the land, before liveried soldiers on foot and horseback stage a 7,000-strong military parade stretching through the streets of the capital.

Much of the two-hour Anglican service, led by the Archbishop of Canterbury Justin Welby, would be recognisable to the 39 other monarchs crowned at Westminster Abbey since 1066.

But while many of the intricate rituals and ceremony to recognise Charles as his people’s ‘undoubted king’ remain, the king has sought to bring other aspects of the service up to date.

There are women as bishops for the first time, while leaders of Britain’s non-Christian faiths and its Celtic languages will play a prominent role.

As king, Charles is supreme governor of the Church of England but heads a more religiously and ethnically diverse country than the one his mother inherited in the shadow of World War II.

He has also sought to make the 2,300-member congregation more reflective of British society, inviting ordinary members of the public to sit alongside heads of state and global royalty.

In another change, the coronation themes mirror his lifelong interest in biodiversity and sustainability.

Seasonal flowers and foliage have been brought, from the wind-battered Isle of Skye in northwest Scotland to Cornwall at the tip of England’s southwest coast, to fill the abbey.

Ceremonial vestments from previous coronations will be reused, and the anointing oil will be vegan.

Britain’s prime minister Rishi Sunak described the coronation as ‘a proud expression of our history, culture and traditions’.

But not everyone is convinced: polling indicates waning support for the monarchy, particularly among younger people.

Charles’s eldest brother Prince Andrew — sidelined due to his friendship with the late convicted paedophile Jeffrey Epstein — was booed as he headed to the abbey.

Overseas, Charles’s position as the hereditary monarch and head of state of 14 Commonwealth countries looks increasingly fragile.

Jamaica and Belize both signalled this week that they are moving toward becoming republics, while Australia, Canada and others may eventually follow suit.

Britons struggling with the soaring cost of living have meanwhile questioned why taxpayers should stump up for the coronation, with the bill estimated to be over $126 million.

Yet the huge crowds of royal fans that have been building all week on The Mall outside Buckingham Palace indicate that the royals still have a central role in British culture and history.

Many of those camping out to watch have flown in from abroad, underlining the royal family’s untouched position as Britain’s leading global brand.

Christine Wilen travelled from Niagara Falls in Canada for the event.

‘I’m very excited to be here, to be part of this history,’ said Wilen, wearing a visor and sweatshirt in Canadian colours.