27 December 2011 Last updated at 02:56 ET

Prince Philip assessed by doctors in hospital

Papworth is the UK's largest specialist cardiothoracic hospital

Doctors are assessing whether the Duke of Edinburgh can return to Sandringham after spending four nights in hospital, during which he missed the Royal Family's Christmas celebrations.

The 90-year-old has been in Papworth Hospital, Cambridgeshire, since Friday, when he had a coronary stent fitted.

He was taken to hospital after he had chest pains while at the Royal Family's Sandringham estate in Norfolk.

Prince Philip had to sit out the traditional Boxing Day shoot.

The BBC's Colette Hume said there seemed to be an increase in activity around the hospital.

"The police have set up a new road block just outside and, although we have not heard anything officially from Buckingham Palace, there seems to be a little change in the atmosphere," said our correspondent.

Earlier, a Buckingham Palace spokesman said Prince Philip continued to make "good progress" following the procedure.

"He remains in hospital under observation and in good spirits," said the spokesman.

The Queen is being briefed regularly on her husband's condition.

On his arrival at Papworth doctors discovered a blocked artery and went ahead with a "minimally invasive procedure of coronary stenting", which was declared a success.

Prince Philip accompanied the Queen to Australia in October

Stenting involves inserting a tube called a stent into an artery, to improve blood flow.

The Duke's next formal engagement is not until 17 January when he is due to attend a dinner at the Scott Polar Research Institute at the University of Cambridge.

Usually on Boxing Day he would lead the Royal Family's shooting party.

But this year he was under doctor's orders not to leave his bed while he was kept under observation.

This is the most serious health scare suffered by the normally spry nonagenarian.

He usually accompanies the 85-year-old monarch and in the autumn he travelled to Australia on a 11-day official visit to Perth, Melbourne, Canberra and Brisbane.