The King will make British history by releasing his personal tax bill to help enhance transparency around royal finances.

The decision – the first by a British head of state – came just days after a brutal poll found support for the monarchy in the UK had fallen to a 33-year-low.

Ipsos polling carried out in March found that 55 per cent of Britons still back a monarchy.

“While monarchists outnumber republicans 2:1, this is the lowest level of support Ipsos has recorded for the monarchy since the series began in 1993 (the previous low was 60 per cent in 2021),” the polling company noted.

The change is being particularly driven by young people, with just 33 per cent of British 18-34 year olds supporting a monarchy, while 45 per cent would prefer a republic.

“Older people remain staunchly monarchist, with 74 per cent of those aged 55-plus supporting a monarchy, just 14 per cent a republic,” Ipsos said.

It also found broad satisfaction with how the King and heir-to-the-throne Prince William are doing their jobs – at 60 per cent and 71 per cent respectively. Further, 60 per cent still believe the monarchy has an important role to play in the future of Britain.

Buckingham Palace announced last week that the King would publish his financial details as his royal household seeks to increase “clarity and accessibility” around the monarchy’s finances.

The decision is in contrast to the Prince William, who has not disclosed the tax he has paid since becoming Prince of Wales and heir to the throne.

“While this is the first time a monarch has shared this personal tax information, you may recall it was similarly released by His Majesty when he was Prince of Wales,” a palace spokesperson said.

“The decision to do so as sovereign has come at the express wish of the King himself, as part of the adaptations carried across since accession.”

The King’s private sources of income could include money from investments or trading profits, funds generated by his private estates of Balmoral and Sandringham and private savings.

The King pays tax on all his private income, and capital gains tax on relevant elements of his assets, as laid out in the Memorandum of Understanding on Royal Taxation 2023, agreed by the government.

His total personal tax information for the 2024-25 financial year will be published later this week, alongside other reports on royal finances.

His 2025-26 tax details will be released next year when their audit has been completed.

Prince William – who celebrated his 44th birthday on Sunday – receives an income from the Duchy of Cornwall, a billion-pound estate that includes The Oval cricket ground and Dartmoor Prison. It provides the heir to the throne with funds independent of the monarch.

The prince received nearly £23 million ($A43 million) last financial year from the duchy and voluntarily pays the highest rate of income tax, once official costs have been deducted. But exactly how much tax he pays has not been disclosed.

The King’s move brought praise from the deputy royal editor of Britain’s Telegraph, Victoria Ward. She said financial transparency had “long been considered a weak spot for the monarchy” and that the King has made a “valiant attempt at turning the tide”.

She said he had inherited an institution from his mother, the late Queen Elizabeth, whose “clandestine operations were deeply rooted in the decade-old mantra of ‘never complain, never explain’”.

But Buckingham Palace is said to hope that the King’s move will “clarify and contextualise” and provide a fuller and more accessible picture.

Also this week, accounts detailing the Sovereign Grant, which funds the official duties of the royal family, will be published at a press briefing alongside a separate extensive new report on royal finances.

Figures from last year showed the Sovereign Grant stood at £86.3 million ($A162.9 million), comprising £51.8 million ($A97.8 million) for core elements such as travel and payroll costs and £34.5 million ($A65.1 million) to fund the Buckingham Palace Reservicing Program.

“Our aim is to explain all elements of royal finances in a way that further enhances clarity and accessibility,” a Buckingham Palace spokesperson said.

“To put it simply: We continue to modernise and evolve.”

-with AAP