The Queen has postponed her Privy Council meeting after being advised by royal doctors to rest, Buckingham Palace says.

The 96-year-old monarch’s latest setback could raise concerns for her health the day after she was pictured in an audience with Liz Truss, as she appointed her as Britain’s new prime minister.

“After a full day yesterday, Her Majesty has this afternoon accepted doctors’ advice to rest,” a palace spokesman said.

“This means that the Privy Council meeting that had been due to take place this evening will be rearranged.”

The Queen remains at Balmoral Castle in Scotland and the latest advice does not involve a hospital stay.

The monarch has ongoing mobility issues and had been due to hold the Privy Council virtually on Wednesday.

During the proceedings, Ms Truss would have taken her oath as First Lord of the Treasury, and  cabinet ministers would have been sworn into their roles and also made privy counsellors if not already appointed as one in past.

There was no constitutional issue with the delay to the proceedings, the palace said.

The smiling head of state looked bright but frail and used a walking stick during Tuesday’s audience, which followed a visit from outgoing prime minister Boris Johnson as he tendered his resignation.

It was the first time in her 70-year reign that the Queen had appointed a prime minister at Balmoral.

The two politicians made the trip from London rather than making the monarch, who has suffered episodic mobility problems since last October, return from Scotland.

The Queen is on her summer break on the Balmoral estate and not due to return until early October.

With her hair neatly curled, the Queen, dressed in a blouse, cardigan and a Balmoral tartan skirt, stood as she met Ms Truss.

The Sun reported recently that the Prince Charles had been making regular morning visits to see his mother as she continued to struggle with her mobility. The unplanned visits are considered highly unusual.

She missed the Braemar Gathering highland games last weekend, which she usually attends each year.

Buckingham Palace has declined to give an ongoing commentary on the monarch’s health.

During her platinum jubilee celebrations in June, the Queen travelled to Buckingham Palace only twice, first for her Trooping the Colour balcony appearance and then for a finale after the pageant.

She spends most of her time at Windsor Castle, 35 kilometres from central London, living there during the pandemic and while major renovations take place at the Palace, and for her comfort.

She secretly spent a night in hospital last October for tests and was then under doctors’ orders to rest for the next three months. That meant she missed the Remembrance Sunday Cenotaph service and COP26 climate change talks.

The Queen caught COVID last February. She suffered mild cold-like symptoms and said the virus left her “very tired and exhausted”.