The Queen is under medical supervision at Balmoral after doctors became concerned for her health, Buckingham Palace said.
A Palace spokesperson said: “Following further evaluation this morning, the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision. The Queen remains comfortable and at Balmoral.”
The Queen’s immediate family members have been informed, with the latest announcement escalating fears for the monarch’s health.
Prime Minister Liz Truss said: “The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime.
“My thoughts – and the thoughts of people across our United Kingdom – are with Her Majesty The Queen and her family at this time.”
The Queen postponed her Privy Council meeting after being advised by royal doctors to rest on Wednesday.
The 96-year-old monarch’s latest setback will raise fresh fears for her health the day after she was pictured in a historic audience with Liz Truss, as she appointed her as the new Prime Minister.
A Palace spokesman said: “After a full day yesterday, Her Majesty has this afternoon accepted doctors’ advice to rest.
“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 Aberdeenshire and the latest advice does not involve a hospital stay.
The nation’s longest-reigning 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 new cabinet ministers would have been sworn into their roles, and also made privy counsellors if not already appointed as one in past.
There is 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 has appointed a PM at Balmoral.
The two politicians made the 1,000 mile round trip from London, rather than making the monarch, who has suffered episodic mobility problems since last October, travel back 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 monarch, dressed in a blouse, cardigan and a Balmoral tartan skirt, stood as she met Ms Truss.
Mr Johnson arrived at around 11.16am and left around 39 minutes later at 11.55am, while Ms Truss arrived at 12.22pm and departed around 33 minutes later at 12.55pm.
The Queen also had another duty afterwards recorded in the Court Circular.
She invested her Communications Secretary Donal McCabe with the Insignia of a Lieutenant of the Royal Victorian Order (LVO), an honour in the monarch’s personal gift for service to the royal family.
A number of guests was also seen leaving the castle before the first audiences began. The Queen often has family members and friends to stay during her annual holiday.
The Sun reported recently that the Prince of Wales had been making regular morning visits to see his mother as she continues to struggle with her mobility, with the unplanned visits 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, the Queen only travelled to Buckingham Palace 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, 22 miles 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 in October undergoing tests and was then under doctors’ orders to rest for the next three months, missing the Remembrance Sunday Cenotaph service and Cop26 climate change talks.
The Queen caught Covid in February, and suffered from mild cold-like symptoms but said the virus left her “very tired and exhausted”.
