Senior members of Britain's royal family are to show a united front Sunday praising the efforts of global health workers before the airing of a tell-all interview with Prince Harry and Meghan Markle.

Just hours ahead of the screening of the interview, which has strained relations between the royals and sparked a transatlantic public relations war, Queen Elizabeth and other senior family members will appear in a programme celebrating the Commonwealth.

Prince Charles, the heir to the throne, his eldest son William and their wives Camilla and Kate will pay tribute to the world's frontline workers in the Covid outbreak.

Charles will commend the "extraordinary determination, courage and creativity" shown by the people of the Commonwealth -- an association of nations from the former British Empire -- while fighting the disease.

He will also say the outbreak has shown how "human health, economic health and planetary health are fundamentally interconnected", emphasising that climate change is another "existential threat" which "knows no borders".

William and Kate, formally known as the Duke and Duchess of Cambridge, will speak with South African doctor and health activist Zolelwa Sifumba about the rights of healthcare workers.

"It's sad, almost, that it's taken the pandemic for the public to really back and support all those working on the front line," Kate will say.

Messages will be broadcast from London's Westminster Abbey, where last year at the Commonwealth Day service Meghan and Harry made their last appearance before giving up royal duties during an acrimonious split from the family. 

They couple, who have relocated to the United States, agreed last month they would not return to their roles as senior royals and said at the time "service was universal".

Since their departure and in the run up to Sunday's interview, counter-briefings in the press between the couple and Buckingham Palace have escalated.

The interview with US chat show host Oprah Winfrey is expected to deal with media intrusion into their lives and the decision to quit royal duties the UK and move to North America.

On Thursday, the US broadcaster CBS released a new clip of the interview in which Meghan said the royal family played an "active role" in "perpetuating falsehoods about us".

Buckingham Palace had said earlier it was probing claims that Meghan had bullied royal household staff during her time in Britain.