On 22 October he was convicted of “cottaging” (“persistently importuning for an immoral purpose”) in a public lavatory just off the Fulham Road. He was fined £10 and advised to consult his doctor. The early 1950s had seen a major increase in the number of convictions for “gross indecency” from less than 300 a year before the war to nearly 1,700 in 1952, over 2,000 in 1954 and more than 2,300 in 1955. All sexual activity between men of any age was illegal and offenders were often given immediate and lengthy sentences of imprisonment.

It was a time when “pretty police officers” acting as “agents provocateurs” enthusiastically engaged in witch hunts which were encouraged and supported by the established Church, the popular press, the then Home Secretary, and the judiciary up to and including the Lord Chief Justice. The list of those arrested included Alan Turing – who helped to break the Enigma code at Bletchley Park – and the author Rupert Croft-Cooke.

Against that background, and focusing on Gielgud’s experience, Nicholas de Jongh has provided a fascinating picture of a now long forgotten and almost unbelievably sexually oppressive society. He takes his title from the then Home Secretary’s public description of homosexuality. In telling his story he uses to great effect the waspish wit which has marked his nearly 20 years as theatre critic of the London Evening Standard. He is greatly helped by Tamara Harvey’s quietly efficient direction, by Alex Marker’s clever multi-scene settings, by performances from John Warmaby as the Home Secretary, Hugh Ross as the Lord Chief Justice and Celia Imrie as Dame Sybil Thorndike. Above all there is Michael Feast who captures brilliantly every nuance of Gielgud’s physical and vocal mannerisms, and who gives a moving picture of a deeply insecure man, almost fatally destroyed by the trauma of his conviction and the resulting prurient publicity. The play ends with a 1975 epilogue in which he is preparing to play the gay Spooner in Pinter’s No Man’s Land.

As a theatre critic it is perhaps not surprising that de Jongh uses Gielgud to make his case, though much more significant at the time were the convictions in 1954 of Edward Montagu, Peter Wildeblood and Michael Pitt Rivers. As they left court to begin their prison sentences the waiting crowd shouted words of encouragement and tried to pat them on the back, having earlier booed and jeered the prosecution witnesses.

The Wolfenden Committee, set up within weeks of those convictions, reported in 1957; a decade later the law began to change, culminating in the 2003 Sexual Offences Act which repealed the “crimes” under which Gielgud and Oscar Wilde were convicted. However Gielgud maintained a dignified silence about the matter. He died at 96 as a national treasure. But he always remained a very private man.

Martin Bowley QC