Sir Keir Starmer has praised the King’s “fantastic” work during his Australia tour, particularly given his “health challenges”.

The prime minister’s comments came after Charles was berated by Australian senator Lidia Thorpe.

At a welcome event in Canberra, she accused the King of “genocide” against her nation’s indigenous people.

At the launch of a consultation on the future of the NHS in east London on Monday, Sir Keir was asked by a reporter if it was “disgraceful” that Australian politicians “are heckling the King”.

King Charles is in Australia with Queen CamillaKing Charles is in Australia with Queen Camilla (Image: Victoria Jones/PA Wire) Sir Keir replied: “Look, I think the King is doing a fantastic job, an incredible ambassador, not just for our country, but across the Commonwealth.”

He said he was looking forward to joining Charles at the Commonwealth summit in Samoa this week, adding: “I think he’s doing a fantastic job, and we should remember in the context of health, that he is out there doing his public service notwithstanding, you know, the health challenges he himself has had – so I think he’s doing a great job.”

King Charles paused cancer treatment to travel to Australia

In February, the King was diagnosed with cancer and paused his treatment to allow him to carry out the long-haul tour to Australia which is his first as the country’s monarch.

 He is also travelling to Samoa for a state visit.

After the King addressed guests at Parliament House, Ms Thorpe, who wore a possum skin coat and carried a traditional message stick, shouted: “You are not our King, you are not sovereign … you have committed genocide against our people.

“Give us our land back. Give us what you stole from us … Our babies, our people. You destroyed our land.”

King lambasted by Australian senator for ‘genocide’ against indigenous people

As she was gently ushered from the building’s hall, Ms Thorpe, who campaigns on First Nations issues, screamed: “Give us a treaty – we want a treaty with this country … This is not your land, this is not your land, you are not my King, you are not our King.”

Ms Thorpe said she was prevented from handing the King a “notice of complicity in Aboriginal genocide” according to the Statute of the International Criminal Court 1998.

She said later in a statement: “The British Crown committed heinous crimes against the First Peoples of this country.

“These crimes include war crimes, crimes against humanity and failure to prevent genocide. There has been no justice for these crimes. The Crown must be held accountable.”

Her outburst overshadowed a speech by the King highlighting his debt to the descendants of Australia’s first inhabitants.

It is understood Charles was unruffled and didn’t let the heckling take away what the royal party considered a positive day in the Australian capital.

Talks of reparations ‘not on the agenda’ for meeting in Samoa

Meanwhile, Downing Street said Sir Keir remains opposed to apologising for the UK’s historical role in slavery and talks of reparations are “not on the agenda” for the Commonwealth Heads of Government Meeting (Chogm) in Samoa.

There is mounting pressure from the leaders of Caribbean nations to pay reparations for the impact of the transatlantic slave trade.

Labour MPs have also reportedly called for the Prime Minister to address the calls as he attends the summit in the Pacific island nation.

However, the Prime Minister’s official spokesman insisted he would not be discussing reparations at the gathering.

“Reparation’s not on the agenda for the Commonwealth Heads of Government meeting,” he said.

“The Government’s position on this has not changed, we do not pay reparations.

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“The Prime Minister’s attending this week’s summit to discuss shared challenges and opportunities faced by the Commonwealth including driving growth across our economies.”

Asked again about an apology, the spokesman added: “The position on apology remains the same, we won’t be offering an apology at Chogm, but we will continue to engage with partners on the issues as we work with them to tackle the pressing challenges of today and indeed for the future generations.”

Following his tour of Australia, the King is attending the summit as head of the Commonwealth.