The royals are two of the King's five counsellors of state, who are authorised by law to carry out official duties for the monarch if he is unwell or travelling abroad.

Counsellors of state include the sovereign's spouse and the next four people in the line of succession who are over the age of 21.

During a sitting in the House of Lords, Viscount Stansgate asked if there were any plans to amend the Regency Act, where these provisions are laid out, now the Duke of York has "left public life" and the Duke of Sussex has "left the country".

He asked if it was time for the government to approach the King to see if a "sensible amendment" can be made.

His comments were backed up by Liberal Democrat Lord Addington, who suggested the first counsellor option should be someone who "actually undertakes royal duties or at least some of them".

"Can the government indicate that they will at least consider that the person they go to in the first consideration will be somebody who actually undertakes royal duties, or at least some part of them, at present?" he asked.

Answering their queries was the Lord Privy Seal, Lord True, who said he would not comment on "specific circumstances" or discuss any "private conversations" that have taken place with the royal household.

However, he added that the government will "always consider what arrangements are needed to ensure resilience" within the country's constitutional arrangements.

"In the past, we have seen that the point of accession has proved a useful opportunity to consider the arrangements in place," he said.

"Obviously, any consideration would also have to take place in close consultation with the royal household."

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Who is allowed to step in for the King?

At the moment, the five counsellors of state are the King's wife Queen Consort Camilla, his eldest son Prince William, his youngest son Prince Harry, his brother Prince Andrew and his niece Princess Beatrice.

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Under the Regency Act, they are able to conduct most of the King's official duties if required, such as attending Privy Council meetings, signing routine documents and receiving the credentials of new ambassadors to the UK.

However, some core constitutional functions are not allowed to be delegated, such as Commonwealth matters, the creation of peers, or appointing a new prime minister.

The dissolving of parliament can only be delegated on His Majesty's specific instruction.

Earlier this year, the authority was used to allow the King, who was the Prince of Wales at the time, to lead the State Opening of Parliament because the Queen was having mobility problems.