The anniversary is expected to be marked privately, given the date is also that of his mother's death at the age of 96.

Britain's Charles III reaches the milestone of his first year as king this week, with his reign so far characterised by a smooth transition from that of his late mother, Queen Elizabeth II.

The anniversary on Friday is expected to be marked privately, given the date is also that of his mother's death at the age of 96.

Charles, 74, has slipped into his new role with apparent ease after some 70 years waiting as her heir — the longest of any in British history.

But despite expectation of reform, he has not yet made sweeping changes to the monarchy, fuelling perceptions that his is a caretaker role before his eldest son and heir Prince William takes over.

"I think the transition has been much smoother than was anticipated," Pauline Maclaran, a professor at Royal Holloway, University of London, told the media.

Charles was officially crowned alongside his wife Camilla on May 6 at London's Westminster Abbey in front of royalty and global leaders.

The lavish ceremony observed centuries-old rituals but was shorter and less elaborate than his mother's in 1953 and aimed to be more representative of modern Britain.

The lavish ceremony observed centuries-old rituals.

"I think we can expect maybe small changes, but he is really paving the way for William, and I imagine William will be the real moderniser of the monarchy," Maclaran said.

Charles remains behind his late mother and 41-year-old William in the popularity stakes, but his approval rating has received a significant boost since his accession.

YouGov polling suggested 55 percent of Britons have a positive opinion of their new head of state, compared to 44 percent a year ago.

His first televised Christmas Day broadcast — a traditional address to Britain and the Commonwealth, which he also heads — was watched by a record 10.6 million viewers in the UK.

Agence France-Presse