One can imagine the fury and sense of betrayal felt by our wartime Queen Elizabeth when she discovered that Anthony Blunt, a man she invited into her home and was entrusted with their precious art collection, was a spy – one of the infamous Cambridge Five.

George VI and his wife were looking forward to spending their first peacetime Christmas since the war at Sandringham House. It had been closed since 1940 and a number of guests were invited.

These included a friend, Dick Molyneux, who the Queen asked in jocular mood if he would “care to come and spend Christmas with us at hideous ugly germ ridden old Sandringham?”

Molyneux accepted happily, and the invitation was  extended to a small group, including Blunt, the newly appointed Surveyor of the King’s Pictures, according to the distinguished author William Shawcross in his  biography entitled, The Queen Mother.

Unbeknown to the royals, Blunt was part of a spy ring that operated throughout WWII, he had been recruited by the KGB, along with Burgess, Maclean, Philby, Cairncross.

His spy masters must have rubbed their hands with glee as Blunt joined his royal hosts in enjoying the festive fun and frivolity, everyone only too happy to brush off the constraints of the terrible war years.

As a lover of the arts, Queen Elizabeth had been anxious about the fate of the paintings and other works of art in the Royal Collection evacuated for safekeeping during the war, Shawcross tells us.

She was involved in bringing them out of their hiding and arranging an exhibition entitled, The King’s Pictures. Blunt played a key role in selecting the paintings for display, indicating he would have worked closely with the Queen during this time. It was an immense success and more than 3666,000 visitors viewed it. Meanwhile, Blunt maintained his treacherous double life.

Its success led to the Queen encouraging the building of a gallery at Buckingham Palace to showcase the Royal Collection on a more regular basis. It opened in 1961 and I have had the pleasure of visiting it on a few occasions.

And Blunt? He had his cover blown in 1964, but in return for not being publicly exposed, he co-operated with his interrogators. He was even able to continue as Surveyor of the Queen’s Pictures – but rumour has it the late Queen Mother would have nothing to do with him.

Mrs Thatcher exposed him publicly on coming to power in 1979. Blunt was stripped of his knighthood that had been bestowed on him and disgraced.

It’s not a story you will find in the Sandringham guide books, a spy who fooled the royals, its tight knit security and British intelligence, and countless others too, but it’s one I feel is worth telling.