The Duke of Edinburgh was described as “comfortable and in good spirits” on his 92nd birthday, following the exploratory operation on his abdomen, Buckingham Palace said.
Philip, who was visited by both the Queen and his son the Earl of Wessex, is progressing according to plans and once out of hospital will spend two months convalescing, stated the Palace.
The Queen visited the Duke on his birthday, arriving at around 7pm and staying with him for around half an hour.
Philip had also received birthday wishes from the Prime Minister.
In a short statement the Palace said: "His Royal Highness The Duke of Edinburgh is progressing according to plans at this early stage. He is comfortable and in good spirits.
"He will remain in hospital for up to two weeks, and it is expected he will then be taking a period of convalescence of approximately two months."
Edward had earlier in the day visited his father and described him as doing "well".
His visit lasted 20 minutes and as he left the London Clinic he was asked by the waiting press how his father was and replied: "Well, thank you".
David Cameron took to Twitter to send a birthday message to the Duke: "Wishing the Duke of Edinburgh a very happy 92nd birthday as he recovers in hospital today."
The King's Troop Royal Horse Artillery fired a 41-gun royal salute at noon in Green Park to mark Philip's birthday, this was followed an hour later by a 62-round salvo by the Honourable Artillery Company at the Tower of London.
Gun salutes were fired around the country from Edinburgh Castle in Scotland to Hillsborough Castle in Co Down, Northern Ireland.
The Duke was admitted to the London Clinic for the pre-arranged operation on Thursday, following a garden party at the Palace that day.
Analysis of the results of the operation are expected to be completed this week, and the Duke is likely to be in hospital for up to two weeks while he recovers.
Details of the original symptoms have not been released, but it is thought the procedure did not involve his heart or bladder, organs the Duke has experienced problems with before.
It is believed that Philip has been visited daily by royal doctor Professor John Cunningham.
Philip's birthday appeared to be remembered by one royal fan who arrived at the London Clinic holding a bunch of white roses, a basket of fruit and a blue balloon with the slogan "Keep calm birthday boy".
The man, who went into the hospital at midday, carried another balloon printed with the message "Feel better".
The 21-gun royal salute at Edinburgh Castle was carried out by officer cadets from City of Edinburgh Universities Officer Training Corps (UOTC), of which the Duke is honorary royal colonel.
Commanding officer of Edinburgh UOTC, Lieutenant Colonel Gordon Mackenzie, said the cadets were thrilled to be part of the pageantry in front of large crowds.
He said: "The officer cadets have just spent two weeks at their annual camp practising everything from survival techniques, building military bridges and conducting peacekeeping operations in a fictional country.
"Firing a 21-gun salute for our royal colonel shows yet another aspect of what university students can experience in the UOTC."