The Duke of Edinburgh's condition has "improved considerably" since he was admitted to hospital on Monday, but he is likely to remain there for the next few days, Buckingham Palace has said.
A spokesman added: "The treatment of his infection continues with antibiotics. He is likely to remain in hospital over the next few days. He is in good spirits."
Philip, 90, is suffering from a bladder infection and is being treated at King Edward VII Hospital in central London.
The illness forced the Duke to miss several key events of the Queen's Diamond Jubilee celebrations, including a service of thanksgiving at St Paul's Cathedral and the concert outside Buckingham Palace.
He was visited yesterday by the Earl and Countess of Wessex, accompanied by their children, Louise and James.
Edward said his father was "feeling a lot better" and had been watching events unfold on television.
Asked how the Queen was coping without her husband, Edward added: "She's bearing up but missing him, obviously."
A large pack of photographers, reporters and television crews remained outside the hospital today.
Three police officers were positioned at the entrance, and vehicles were prevented from parking near the building.