The Duke of Edinburgh will miss the Queen's Diamond Jubilee celebrations today as he remains in hospital with a bladder infection.

Philip, 90, was taken to the King Edward VII Hospital in London from Windsor Castle yesterday as a precautionary measure.

He will remain in hospital under observation for a few days, a Buckingham Palace spokeswoman said.

Three police officers stood guard at the main entrance to the hospital this morning while other exits were also guarded and a police van was parked to the side.

A number of members of staff were seen entering the building while a man dressed in a morning suit got out of a taxi and went inside.

A large pack of press were huddled together behind a barrier facing the private hospital, which had a Union flag flying from it.

The Prince of Wales paid tribute to his father last night as he addressed the crowds gathered for the Diamond Jubilee concert at Buckingham Palace.

"The only sad thing about this evening is that my father cannot be here with us because unfortunately he's been taken unwell," he said.

He added: "Ladies and gentlemen, if we shout loud enough he might just hear us in hospital."

A huge cheer went up from the spectators and many stamped their feet and chants of "Philip, Philip" broke out.