‘In the prison of his days,’ W.H. Auden wrote, ‘teach the free man how to praise.’ Noël Coward’s last performance, possessing, like so much of his work, a scene-stealing quality, was in the 1969 film The Italian Job. He plays the gangster Mr Bridger, masterminding a gold robbery from his Turin prison cell. In his final appearance he walks like a Ziegfeld heroine down the central stairs of the jail to the fervent acclamation of the other inmates, acknowledging the ovation to left and right. Coward had abundant worldly acclaim; and he knew very well where the walls lay, and the doors that would not be breached.

That knowledge has served him extremely well. Many of his contemporaries thought that his dedication to the ephemeral, responding to the fads of the moment, would prove fatal to his claims on posterity. The opposite has proved to be the case. Though most of his 50-odd plays are forgotten, the best of them are indestructible: Blithe Spirit, Private Lives and Hay Fever are universally acknowledged masterpieces, and others turn up regularly, including Design for Living, Present Laughter and The Vortex. In Which We Serve and Brief Encounter are classics of the cinema; and dozens of the enchanting songs have held their own. His impact was immediate, and enduring. The repartee in Waiting for Godot and Endgame, or in many of Harold Pinter’s plays, owes much to the absurd exchanges in Private Lives. And what is the hit TV series Schitt’s Creek but six seasons of Hay Fever?

He was extraordinarily original. Hay Fever may be squarely within the sublime English tradition of stage comedies about precisely nothing, but its cadences are astonishing. Has there ever been a curtain fall like the one at the end of the first act, with the characters’ small talk failing, and them staring at each other aghast? Coward went on being innovative, even when fashion turned against him. His 1947 play Peace in Our Time was, Oliver Soden thinks, the first of a long line of counterfactual literature based on the premise that the Germans won the war and occupied England. Other plays revolved around different groups of people in the same space at different times, or explored actors living together in a care home, still performing and dwelling on past glories.

This is a fine biography. It’s the fourth full-length one of Coward to appear, Philip Hoare’s, published nearly 30 years ago, being still one of the best. But Masquerade is justified because changing attitudes mean that more can be discussed – Coward’s first biographer was forbidden to talk about his sexuality – and because material keeps emerging. Soden’s previous work was a terrific life of Michael Tippett, and it must have struck him what very different characters the two men were – though both were composers, both innovative and devoted to finding new ways of existing, and both lived through the same period when homosexuality was proscribed.

The challenge for Coward’s biographer is to get through to what the man was really like – and I’m not sure it can be done. From the very start he was ‘on’, performing for other people’s amusement. His first letter, written at the age of eight, is a childishly adorable performance in itself, as he reports for his mother’s benefit that, visiting a prosperous aunt: ‘I dressed up in a short dress and danced to them and sung to them.’ There are just glimpses of an inner self later when, exhausted, he occasionally burst into tears on stage. For the rest, everything is put on.

Much of the task is to sort out the authentic stories from those that have accumulated around his famous wit. Soden doubts whether Coward had an affair with George, Duke of Kent, or even made the joke about the Queen of Tonga’s lunch; and other celebrated lines are passed over in silence. (I regret the absence of his explanation to an inquiring child that ‘the doggie in front has gone blind, and his friend is pushing him all the way to St Dunstan’s Hospital’.)

The quality of performance, however, is everywhere. A message of love is an opportunity to entertain – such as his telegram to Gertrude Lawrence on her wedding day: ‘Dear Mrs A., Hooray, hooray, At last you are deflowered. On this as every other day I love you – Noël Coward.’ The carapace may be impossible to pierce, now as it was then. Even touring Burma during the war in monsoon season, under fire from the Japanese and falling flat on his face in the mud, the worst that could be got out of him was: ‘I’m most frightfully sorry, but it’s the fucking awful weather.’

That impregnable performing quality was a source of strength, which got a seeming butterfly through situations in which more obvious heroes would crumple. As Auden very truly observed, it’s the ‘pink and white/fastidious, almost girlish’ types who cover the retreat when ‘the proud-arsed broad shouldered break and run’. Soden emphasises what Coward achieved through sheer cheek, taking 1920s London by storm by writing about totally unacceptable subjects in ways both shocking and extremely funny. There was also a lot of turning up without being invited, for which someone as amusing as Coward was usually forgiven. And there was a lack of respect for status; despite his friendships with royalty, he was not a snob especially. He liked clever people, but poked fun at pretension. His career was given an early boost by his brilliant stage parody of the Sitwells (in the guise of Gob, Sage and Hernia Whittlebot), and Edith’s poetry performances:

Round – oblong – like jam –
Terse as virulent hermaphrodites;
Calling across the sodden twisted ends of Time…

Cheek, and a determination not to take no for an answer, bore fruit in what can only be described as a good war for Coward. Through his connections, he found himself admitted to the intimate circles of the Churchills and the Roosevelts – after a visit to the latter, he was summoned to the presidential bedroom to say goodbye. But it was certainly a challenge to do all that he wanted. The prejudices of the time extended from Joyce Grenfell (‘It is definitely a pity that the man who represents this country should be famous as a queer’) to that notorious stinker and closet queen Hugh Dalton (‘of course he is a roaring pansy’). Those kind of obstacles made it impossible for him to continue some initially successful informal approaches, drumming up support in America and across the Empire.

Instead, he devoted himself to gruelling tours, entertaining the troops and keeping up spirits in what were often his most admired productions. In Which We Serve was a dazzlingly innovative film (the studio conditions under which it was made were worse than the actual navy, according to Mountbatten). There were also daring ventures in what might have been question-able taste: Churchill adored the song ‘Don’t Let’s Be Beastly to the Germans’, and we are reminded how extraordinary the closing tableau of Blithe Spirit must have been to its first audience in 1941, the set being destroyed around Charles Condomine as London outside the theatre was being threatened with total destruction.

This is a sympathetic and very touching biography. Soden makes the daring decision to write occasional sections in imitation of Coward’s style. Not every biographer would be up to this, but Soden pulls it off. The ending is particularly good – first skating around Coward’s last days, letting him evaporate like Elvira, then giving us a chorus of biographers, boyfriends and household servants to narrate it in detail. But the whole book is beautifully done, and will last – at least until more material surfaces. Are some official files relating to Coward’s wartime activity still to be opened? He was engaged in quite secret work, as well as having intimate connections with royalty, among other dignitaries, and information of that sort can remain closed for a long time.

Coward got away with an extraordinary amount. His only brush with the law had nothing to do with his private life and his chain of boyfriends but with a financial matter (which one of the boyfriends had hopelessly mismanaged). And, naturally, he would be forgiven. In 1924, George V was involved in a decision of the Lord Chamberlain about The Vortex, and said the play sounded ‘disgusting’; but seven years later, the king and queen with their entire family made a rare outing to the theatre, to set the seal of approval on Cavalcade.

Coward’s life demonstrates unequivocally that you might as well give anything a go, and the worst that can happen is you will be told no. There was a fair amount of that during his long career. But in the end there was, also, the second greatest balcony scene in English literature; the line in Blithe Spirit when Madame Arcati proposes one more séance – ‘really putting our backs into it this time’; and the moment when the barometer falls off the wall in Hay Fever. Those things survive when serious disquisitions about politics and philosophy and significance prove as ephemeral as an ice cube in a glass of flat lemonade. There’s every reason to think Coward will last forever – and this excellent biography is just what he deserves.