Buckingham Palace has been urged to disclose documents that would reveal the truth about the relationship between the royal family and the Nazi regime of the 1930s.
The Sun's decision to publish footage of the Queen at 6 or 7 years old performing a Nazi salute, held in the royal archives and hitherto unavailable for public viewing, has triggered concerns that the palace has for years sought to suppress the release of damaging material confirming the links between leading royals and the Third Reich.
Unlike the National Archives, the royal archives, which are known to contain large volumes of correspondence between members of the royal family and Nazi politicians and aristocrats, are not compelled to release material on a regular basis. Now, as that relationship becomes the subject of global debate, historians and MPs have called for the archives to be opened up so the correspondence can be put into context.
"The royal family can't suppress their own history forever," said Karina Urbach of the Institute of Historical Research at the University of London. "This is censorship. Censorship is not a democratic value. They have to face their past. I'm coming from a country, Germany, where we all have to face our past."
The Sun was subjected to a backlash on social media after publishing 80-year-old home movie footage from the grounds of Balmoral Castle, in which a laughing Princess Elizabeth, her mother, Prince Edward (later Edward VIII) and Princess Margaret were shown making Nazi salutes.
Barbara Keeley, Labour MP for Worsley and Eccles South, retweeted a message that read: "Hey @TheSun, if you want to stir up some moral outrage about a misjudgment in history, look a bit closer to home."
Many expressed incredulity that the paper had published the actions of a child. But managing editor Stig Abell defended publication. "It is an important and interesting issue, the extent to which the British aristocracy - notably Edward VIII, in this case - in the 1930s, were sympathetic towards fascism," he said.
Urbach, author of Go-Betweens for Hitler, a new book about the relationship between the royals and the Nazis, has spent years trying to gain access to documents relating to Nazi Germany held in the royal archives.
She described the archives, in Windsor Castle's Round Tower, as "a beautiful place to work but not if you want to work on 20th-century material . . . you don't get any access to anything political after 1918."
She described seeing shelves of boxes containing material relating to the 1930s that no one is allowed to research. She also suggested that much of the archives' interwar material no longer existed.
"We know that after '45 there was a big clean-up operation," Urbach said. "The royals were very worried about correspondence resurfacing and so it was destroyed."
Helen McCarthy, a historian of modern Britain at Queen Mary University of London, echoed Urbach's comments, tweeting that "if Royal Archives were more accessible & welcoming to researchers, 'shock' discoveries like Sun's front page could be put in better context".
Historian Alex von Tunzelmann suggested on Twitter that the lack of access to the royal archives for both historians and the public "is profoundly undemocratic".
"We need much greater access. We need to be grown up about it. The history of this country belongs to the public."