Fears are growing after Prince Philip and his family were warned he could be kept in hospital for up to six weeks while he is treated for an underlying condition.
The Duke of Edinburgh was admitted for heart tests as he continued to battle a raging infection.
He was moved by ambulance at around 11am from the private King Edward VII hospital in Central London to St Bartholomew’s, Britain’s oldest hospital near St Paul’s Cathedral, the Mirror reports.
Staff held up umbrellas to ensure the Duke’s privacy as he was carried by stretcher to the waiting vehicle.
A royal source said: “The staff and all the Royal Family are united in their prayers for the Duke.
“There has been an almighty and collective effort to keep him and the Queen safe during the coronavirus crisis over the past 11 months but there was a significant shift in the mood when everyone started finding out the Duke wasn’t coming home any time soon.
“Everyone’s thoughts are now firmly centred on him pulling through this illness.”
Buckingham Palace said: “The Duke remains comfortable and is responding to treatment but is expected to remain in hospital until at least the end of the week.”
But medical experts tonight suggested the Duke could be in hospital for “four to six weeks” and given intravenous antibiotics if he has a heart infection.
NHS cardiologist Dr Aseem Malhotra said: “It’s more likely he had an infection elsewhere.
“It could’ve been in the urinary tract or a chest infection and the stress on his body put strain on his heart.
“Therefore he had to be taken to a specialist cardiac centre to make sure heart is functioning while he is treated for the infection. What makes it more likely is his underlying heart issues.
“This is all speculation and it’s difficult to draw conclusions with the limited information.
“He’s far healthier than the average person of his age and is clearly a very robust and resilient man.
“I wish him very well and hope he gets better soon.”
Doctors at St Barts – based at the state-of-the-art King George V building which is Europe’s largest specialised cardiovascular centre, will continue to treat Philip for the same infection as well as performing tests and observation on his heart.
The hospital has a specialist heart attack centre which delivers dedicated emergency care 24 hours a day, with rapid access to a team with specialist expertise and equipment.
The NHS said the centre aspires to perform more heart surgery, MRI and CT scans than any other service in the world and gives patients world beating care across 10 theatres, 10 specialist laboratories and more than 300 general, cardiac and critical care beds.
It is not known what type of infection the Duke was suffering from for “several days” before he was admitted on February 16, but he has suffered from bladder infections in the past.
At Christmas in 2011 he also had an operation to clear a blocked artery in his heart after being rushed to hospital with chest pains.
Buckingham Palace had previously said the Queen’s consort was staying in hospital for “rest and recuperation” and only admitted “with an abundance of precaution”.
A week later aides revealed the royal – who turns 100 in June – was being treated for an infection but “responding well to treatment”.
Philip has been visited by Prince Charles, 72, on the first weekend he was in hospital and could be visited by other members of the family in the coming days.
Last Tuesday, when it was announced the duke would spend several more days in hospital being treated for the infection, the Earl of Wessex said he had talked to his father on the phone and he was “a lot better”.
Philip is known for his “no fuss” attitude and to not suffer fools gladly, and Royal biographer Penny Junor said his demeanour in hospital would be important.
She said: “Let’s hope he’s not resigned, let’s hope he’s not being a good patient because I think that would probably be a bad sign – a cantankerous duke is a healthy one.”