Prince William joins the vigil of the Queen Mother's coffin in Westminster Hall

At exactly 5.40pm on Monday, the 8th of April 2002, the four grandsons of the Queen Mother walked silently into Westminster Hall.

Minutes before the royal party appeared, a hush descended on the hall as mourners filing past the coffin came to a halt.

Then Prince Andrew appeared, his medals and the gold braid of his naval uniform glinting.

Viscount Linley, the son of Princess Margaret, came next followed by Prince Charles and Prince Edward. They were all sombre and Charles seemed as devastated as he was when he marched behind the Queen Mother’s coffin during the lying-in-state procession.

It was his idea to re-enact the poignant vigil held by King George V’s sons in 1936. That tribute was held in private. But Charles was insistent that yesterday’s should be in full public glare.

At least 400 people watched the four take up their positions in a formal and intricate military procedure.

They stepped towards the four corners of the dais then stood in silence, hands clasped, heads bowed. Also there, watching from a gallery, were Prince William, Prince Harry, Princess Anne, her husband Commander Tim Laurence, her son Peter Phillips and Sophie Wessex. As they took their places, they turned to the coffin and bowed solemnly.

Mourners then began to file slowly past - around 1,000 of them during the grandsons’ 20-minute vigil. MPs and peers such as former Prime Minister Lord Callaghan walked alongside teenagers in jeans. Mums pushed babies in prams. Children stopped to gawp as embarrassed parents tried to hurry them along.

For many the presence of the grandsons, standing completely still, so proud, added to the emotion. And they began to cry.

Despite the potential distractions the four around the coffin remained composed, their eyes cast down. William and Harry stared at ashen-faced Charles, hands clasped around his sword - and seemed moved by the nature of his tribute.

The grandsons had paid extraordinary attention to detail.

The shoes of Lord Linley and Prince Edward had been polished to a glass finish. Their morning suits were immaculate.

The brass buttons on the uniforms of Andrew and Charles gleamed. Candlelight reflected from their shining swords.

Still the people came, some carrying Union flags. Many were surprised to see the grandsons and stopped in their tracks, gasping.

Towards the end of the vigil William and Harry led the royal party from the gallery to join the queue. They did not rush to the front of the line but joined at the back, waiting patiently for their turn.

The move delighted the well-wishers. Some leaned forward to whisper their condolences. Princess Anne turned to thank them. Once or twice, William and Harry glanced up at the stone statues of Saxon kings looking down on them from the walls.

As they passed by their father they bowed their heads, looking at him anxiously. They bowed again as they passed the coffin before heading outside into the glare of a courtyard.

A thronging crowd applauded as they appeared. Some shouted 'God Bless' as the young princes chatted to other mourners leaving the hall.

The vigil came to an end when Big Ben struck six. As it did so, the Queen’s broadcast to the nation began on TV.

In the hall the grandsons’ places were taken by four Yeomen of the Guard. The four relinquished their positions and emerged into the courtyard.

The solemn vigil by the Queen Mother’s grandsons was inspired by a ceremony mounted at Westminster Hall 66 years ago after the death of George V.

On January 27, 1936, the new King Edward VIII and his brothers Albert, Henry and George stood guard around the old king’s coffin.

Their silent Vigil of the Watch tribute was echoed yesterday in a 20-minute ceremony just before the Queen’s emotional TV address to the nation.

Princes Charles, his brothers Andrew and Edward and Princess Margaret’s son Viscount Linley arrived in two cars shortly before 5.40pm.

Charles, 54, wore the dress uniform of a rear Admiral and Andrew, 42, that of a Royal Naval commander. Edward, 38, and Lord Linley, 40, each wore morning coats.

Charles and Edward walked to the right of the coffin, while Andrew and Lord Linley walked to the left.

With military precision, all four turned inwards and walked up the steps of the dais supporting the catafalque.

Charles and Andrew briefly rested both hands on their ceremonial swords.

And all four grandsons stood in silence with their heads bowed.

The royal vigil had originally been intended to be held in private. But the sheer number of people waiting to see the Queen Mother sparked a change of plan and mourners were allowed to file past as the royals kept watch.

More than 200,000 people have queued to mourn the Queen other at Westminster Hall.

And at least 400,000 saw the coffin as it was brought there from St James’s Palace to Westminster Hall on the 5th April.