In the aftermath of the image recently published in the Sun, historians are rightly calling for material hidden away in the archives at Windsor Castle to be made publicly available so we can learn more about the relationship between the Royal family and fascist Germany during the 1930s. During my own research into the history of theatre censorship in Britain during this period, I was allowed to see a little of what’s held in the Round Tower, and these documents, alongside the hundreds of censorship files held in the British Library archive – stuffed full of correspondence and memoranda – shed light on one aspect of that relationship.

From 1737 until 1968, theatre censorship was in the hands of the Lord Chamberlain, a senior servant in the royal household and responsible to the monarchy. No new play could be publicly performed without being first licensed by him, and he could either ban plays or demand changes as he saw fit.

The Lord Chamberlain was not obliged to supply reasons for his decisions, or to follow any criteria other than his own whims, and because he was part of the royal household he was not even answerable to parliament. It was a system that had been introduced by the prime minister Sir Robert Walpole, who wanted to prevent criticism of his government from the stage. And while censorship was often linked to moral issues (in the early 20th century Oedipus was banned in case it inspired audiences to go home and commit incest), it was also applied for political reasons – even Noel Coward saw his plays banned in the 1920s because of fears that their depiction of a decadent upper class might encourage working-class revolution. In an age when there was no television and little radio, theatre was seen as second only to the press in its influence; as one MP put it, “young men and young women form their ideas of what is right and wrong in no small degree from what they witness on the stage.”

In the past few days, the claim has been made that people in Britain in 1933-34 knew little about what was going on in Nazi Germany. Of course a six-year-old child would have known nothing – but this is not true of adults. Some playwrights certainly did. But the key point here is that such playwrights were prevented by the Lord Chamberlain from expressing what they wanted to say. Between 1933 and 1939, Lord Cromer, who held the office, regularly intervened to silence overt criticism of the Nazis, or depictions of Hitler and other German leaders.

The records show that in borderline cases he not only consulted the British Foreign Office, but also sent scripts to the German embassy for a “friendly German” to advise him. While I have seen no hard evidence that he discussed plays with members of the Royal family, we can be pretty sure that he knew what they would want. He was, after all, their servant, and his other duties included accompanying the monarch on state visits and organising garden parties at Buckingham Palace, as well as supervising the annual upping of the royal swans.

Cromer’s decisions on theatre censorship in the 1930s were governed by the bizarre assumption that because any script must be given permission by the monarch, it followed that the views expressed in the play were not simply those of an individual playwright, but were shared and supported by the King. Criticising a friendly power – as Germany was – or its leader, would have been unacceptable. Moreover, as Cromer often warned, Germany might respond by criticising Britain and Britain’s rulers.

Lording it over us: Lord Cromer, left, at a meeting of the state advice office in Downing Street, November 1936. Photograph: Imagno/Getty Images

It’s worth looking at a couple of examples of the Lord Chamberlain in action. In August 1933, a play was submitted by a Jewish doctor from Leeds; it was set in a country called Nordia, which was ruled by a dictator named Hacker and his antisemitic Yellow Shirts. The playwright told the Daily Express that his script was “based entirely on first-hand information”. The script reader employed by the Lord Chamberlain described the play as “a strong indictment of the atrocities and excesses committed by the Nazis”, but recommended that since it was “aimed at atrocities denounced by every English newspaper, by many public men, by the overwhelming majority of English people in private, it would be in my opinion a great mistake to ban it.”

But ban it is just what the head of the royal household did: “Whatever one may think of the Hitler regime, the prosecution of Jews etc. they are no direct concern of ours,” he wrote, adding: “At the present time it would be an unwise play to produce and will do no good, only possibly harm.”

In February 1934 Lord Cromer rejected another anti-Nazi play, even though the producer offered to make any cuts and changes he might require. It was not that Cromer doubted the accuracy of the play – far from it: “The brutality of the Nazi regime is, I imagine, beyond question... [but] it would be very mistaken policy to allow such plays to be acted on the English stage.” And a few months later he noted, pointedly, that it was “not easy to go on shielding the Germans from their misdeeds being depicted on the stage in this country.”

Some criticisms of Germany did make it on to the stage, where they could be sufficiently masked and not too explicit. In 1938, Auden and Isherwood’s On the Frontier was rather reluctantly approved amid disagreements in the Lord Chamberlain’s Office in St James’s Palace: “To forbid this would be to subscribe to fascist ideology”, insisted one of his readers, who had become increasingly frustrated at the decisions being made by his superior. But what actually saved this play, so far as Lord Cromer was concerned, was that it could be read more as anti-war than anti-Hitler, with the democratic nation as guilty of war-mongering and nationalistic propaganda as the dictator-led regime. And as late as July 1939, the Lord Chamberlain banned a play because he considered it “a violently prejudiced piece of special pleading” which “spares no pains to vilify the Nazis and exalt the Jews”.

The video obtained by the Sun of the young Queen, which has prompted calls for further investigation into the links between the royal family and the Nazi party.

It’s hard to know how important it was that playwrights were largely prevented from commenting on Nazi Germany during the 1930s. (The press was free of such restrictions, so writers and cartoonists could say what they liked – or at least what their editors and proprietors would allow). But the way in which the British monarchy used the Lord Chamberlain to protect Nazi Germany from attack or criticism on stage should at least be taken into account when assessing their relationship.

A brilliant satirical farce co-written by a young Terence Rattigan was repeatedly refused a licence until after war had been declared – by which time its moment had passed. In August 1939, Cromer had sent the script to the German embassy, who advised him that he should ban the play because it would not “be helpful in improving Anglo-German relations.” As for the fun of Nazi salutes, a comedian in a pantomime who dared to mock Hitler with a five-second goose-step march and a Sieg Heil chant in his role as a pirate leader in Robinson Crusoe was taken to court and fined after the Nazis at Belgrave Square complained to St James’s Palace.

• Steve Nicholson is Professor of Theatre at the University of Sheffield. He is the author of The Censorship of British Drama 1900 to 1968.

