The Queen and Prince Philip have been taken to their country residence by helicopter after delaying travel plans for a day through ill health.
Buckingham Palace said both were suffering heavy colds.
Elizabeth, 90, the world’s longest-reigning living monarch, and her husband Philip, 95, had been due on Wednesday to catch a train from London to their Sandringham residence in Norfolk where they traditionally spend Christmas.
The couple, who have been married for 69 years, were well enough on Tuesday to host members of the royal family for a lunch at Buckingham Palace including Princes Charles, William, and grandson George.
After six decades on the throne, the Queen has cut back on international tours but still regularly performs official duties around Britain, although she said on Tuesday she would reduce the number of her patronages.
Although Elizabeth’s father, George VI, died at the relatively young age of 56, her mother, who was known as Queen Elizabeth the Queen Mother, lived until 101 and was still appearing in public almost up until her death in 2002.
Both the Queen and Prince Philip’s good health has allowed them to remain very much in the public eye, despite their age.
The Times reported on Wednesday that Philip carried out more public engagements last year than did his grandsons Princes William and Harry, and William’s wife Kate combined.