Charles III will visit Westminster Hall on Monday morning in his first visit to parliament as the new monarch following the death of his mother Queen Elizabeth II.
Both Houses of Parliament will express their condolences to the King and his wife Camilla, the Queen Consort, in a ceremony known as the presentation of addresses.
Commons Speaker Sir Lindsay Hoyle and Lords Speaker Lord McFall will give addresses on behalf of MPs and peers, before Charles gives his reply.
The 10am ceremony will be attended by MPs – including the new prime minister Liz Truss – peers and members from the legislatures of Northern Ireland, Scotland and Wales.
It takes part in the oldest part of parliament, Westminster Hall, which has hosted Henry VIII’s coronation banquet and Guy Fawkes’s trial.
Ms Truss will support the King by joining him at “services of reflection” in Scotland later on Monday, before joining him at services in Northern Ireland and Wales later this week as part of the 10-day mourning period.
The prime minister’s official spokesperson said Ms Truss believed it was “important to be present” at the services, but No 10 later pushed back against suggestions the PM was accompanying Charles “on tour”.
Though a constitutional monarch must remain politically neutral, Charles’s role will consist of holding regular audiences with the PM and assenting to bills passed by parliament on the advice of ministers. Royal Assent has not been refused since 1707.
David Cameron, former Tory prime minister, has said he thought it was “entirely right” for the King to have written to ministers with his views when he was Prince of Wales.
Speaking to the BBC, Mr Cameron said the so-called “spider memos” of letters to ministers on various issues from herbal medicine to badger culls – which were released in 2015 after a lengthy legal battle – should have stayed private.
“I never felt he tried to influence me improperly in any way,” he told the Sunday with Laura Kuenssberg programme. “I think the heir to the throne has a perfect right to have an interest in issues like the environment, preserving wildlife, his interest in the built environment.”
Mr Cameron added: “I think it is entirely right that the heir to the throne can discuss things with politicians. Why not? I don’t think there should be any public concern about that, and my view is the letters should have remained private.”
Former Labour prime minister Gordon Brown said Britain could become more like a “Scandinavian monarchy” – saying he expected Charles to perform his duties in a less formal way as part of a slimmed-down royal family.
Charles will lead the royal family in a poignant procession behind the coffin of his mother when it travels to an Edinburgh cathedral this afternoon to allow the public to pay their respects.
The Queen will be taken to nearby St Giles’ Cathedral where her family will attend a service of thanksgiving for her life. Charles will later meet Scotland’s first minister Nicola Sturgeon and receive a motion of condolence at the Scottish parliament.
