Millions watching the coronation are to be asked to swear allegiance to King Charles III, with the public given an active role in the ceremony for the first time.

His coronation will include the first Homage of the People.

Lambeth Palace said it was hoped the change to the service will result in a “great cry around the nation and around the world of support for the king” from those watching on television, online or gathered in the open air at big screens.

It replaces the Homage of Peers, in which a line of hereditary peers knelt and made a pledge to the monarch in person.

The liturgy — words and actions of the coronation service — have been revealed, having been decided upon in consultation with King Charles, the Archbishop of Canterbury Justin Welby and the government.

The archbishop will call upon “all persons of goodwill in the United Kingdom of Great Britain and Northern Ireland, and of the other realms and the territories to make their homage, in heart and voice, to their undoubted king, defender of all”.

The order of service will read: “All who so desire, in the abbey, and elsewhere, say together:

“All: I swear that I will pay true allegiance to your majesty, and to your heirs and successors according to law. So help me God.”

It will be followed by a fanfare.

A spokesman for Lambeth Palace, the archbishop’s office, said: “The Homage of the People is particularly exciting because that’s brand new.

“That’s something that we can share in because of technological advances, so not just the people in the abbey, but people who are online, on television, who are listening, and who are gathered in parks, at big screens and churches.

“Our hope is at that point, when the archbishop invites people to join in, that people wherever they are, if they’re watching at home on their own, watching the telly, will say it out loud — this sense of a great cry around the nation and around the world of support for the king.”

The words printed in the service are for “everyone to share in”, the representative said.

Before the Homage of the People, the archbishop will pay homage representing the Church of England, followed by the Prince of Wales — performing what is the only Homage of Royal Blood.

Just like his grandfather Prince Philip did for his wife Elizabeth II at her coronation, Prince William will kneel before the monarch, place his hands between his father’s hands and vow to be his “liege man of life and limb”.

He will say: “I, William, Prince of Wales, pledge my loyalty to you and faith and truth I will bear unto you, as your liege man of life and limb. So help me God.”

The symbolic act means the heir to throne, as ‘liege man’ to the king, has a mutual obligation to the monarch.

In the past, other dukes of royal blood would pay homage, but this time, with only William taking part from the royal family, it removes the need for the dukes of Sussex and York to undertake this role.

The removal of the homages of hereditary peers also has the benefit of helping to reduce the length of the service, which is now two hours instead of around three as it was at the late queen’s coronation.

William has another duty during the service.

He will enter the coronation theatre earlier in the ceremony in the investiture segment and help clothe the king in the robe royal, also known as the mantle, before the crowning.

William will join Baroness Merron, former Board of Deputies of British Jews chief executive, and help bishops to lift the “robe of righteousness” on to his father.

The robe represents what the king, as sovereign, has been given by God.