In our fierce, overheated world of self-revelation and exposure, where you can read of the intimate lives of not only the rich and famous, but the obscure and infamous, Coward's attitude seems increasingly enviable. His is a world of our parents' generation, a world rapidly disappearing as we leave the century behind, a world of different values, and different voices.
In my turn-of-the-century Chambers Dictionary - published in the year of Coward's birth, one of the definitions of reticence is "concealment by silence". The last completed play Coward wrote was A Song At Twilight, revived this month by Sheridan Morley at the King's Head Theatre. It is an intricately woven tribute to Coward's own reticence, and that of Somerset Maugham, on whom the play's irascible main character is based.
Hugo Latymer, a married, aged writer, is suddenly faced with evidence of his homosexuality produced by a former (female) lover. "Homosexual tendencies in the past?" she retorts. "You're queer as a coot and you have been all your life." Here, towards the very end of his own life, Coward appeared to be questioning his own emotional reticence at a time when homosexuality was about to be decriminalised, and when the "plays with a message" Coward hated (if invited to attend one such, he'd quote an actress friend who declared, "Then I shan't dress") of Osborne, Pinter et al challenged that very reticence.
For Coward, sex and sexuality was always a matter of good taste. When a New York friend took him to the openly gay resort of Fire Island in the mid-Sixties, he was appalled: "I have always been of the opinion that a large group of queer men was unattractive. On Fire Island, it is more than unattractive, it's macabre, sinister, irritating and somehow tragic." How much more shocked would The Master have been to walk down present-day Old Compton St, or Manchester's gay village. For Coward, the point was one of exhibition. "Taste may be vulgar," he declared, "But it must never be embarrassing. There is no need to embarrass anyone."
Coward's approach finds echoes with a more recent, and apparently outre gay media figure: Boy George. Coward, in his autobiographical play of 1939, Present Laughter (currently revived at the West Yorkshire Playhouse with Ian McKellen in the central role), announced, a propos of sex: "To me the whole business is vastly over-rated. I enjoy it for what it's worth and fully intend to go on doing so for as long as anybody's interested and when the time comes that they're not I shall be perfectly content to settle down with an apple and a good book!" Boy George - the Queen Mother of Pop - announced in the sexually overt 1980s that personally, he preferred "a nice cup of tea".
It was an almost shocking statement for the time, and is counterpointed by George Michael's recent appearance on the Parkinson Show, when he spoke openly of sex in public lavatories in a manner which seemed to mark a sea-change in the attitudes of Blairite Britain: the pop aristocrat as pop philosopher, personifying a new morality apparently condoned by a venerable, highly-respected representative of old TV (and, indeed, by his association with that other exemplar of overt emotionalism, the late Princess Diana).
In 1929, Coward wrote the defining lyric of his career: "If Love Were All". Sung by the heroine of Bitter-Sweet, it is nonetheless, in Coward's voice (and indeed in the Pet Shop Boys's recent cover of the song) a cri de coeur: "Life is a very rough and tumble/For a humble/Diseuse/ One can betray one's troubles never/Whatever/Occurs/Night after night/Have to look bright/Whether you're well or ill."
"Subtlety, discretion, restraint, finesse, charm, intelligence, good manners, talent and glamour still enchant me," he declared 30 years later, with the unequivocation of one who had been a Bright Young Thing, an exemplar of an era in which emotion was masked because so much emotion had been suffered - in the Great War. Indeed the enormity of the war seemed to have had an effect on the British psyche: the soldiers who had to retreat behind taciturnity in the face of the horror of their experience.
Language, for Coward and his generation, was a defensive weapon - it is no coincidence that his speech was so clipped and quickfire that it sounded like a Gatling gun going off - while what was said was so often the opposite of what was meant. Private Lives is more emotional because of the self-denial of the characters' emotions (reticence, after all, is a come-on).
"Words. Masses and masses of words!", says an exasperated Myra in Hay Fever; "We none of us ever mean anything", confesses an equally exasperated Sorel in the same play. Or as Leo declares ("grandiloquently" as the stage directions demand) in Design For Living: `It's all a question of masks, really; brittle, painted masks. We all wear them as a form of protection; modern life forces us to. We must have some means of shielding our timid, shrinking souls from the glare of civilisation."
That mask, assumed with increasing regularity throughout Coward's life as the progression of the 20th century piled up upon him, would present a formidable obstacle to would-be biographers. When I wrote my biography of Coward, five years of research produced little concrete evidence of his many affairs with men. As these were supposed to include names as diverse as James Cagney and the Duke of Kent (Prince George, the present Queen's uncle), this was frustrating, to say the least.
But perhaps it is as it should be. Coward's putative affair with Kent has never been proved; but the suspicion of it lends glamour to his image: Coward sobbing at the news of the Duke's accidental death in a wartime aircrash: the snide, but rather witty comment from a friend, "You know, Noel, you can never be the Dowager Duchess of Kent". Nowadays The Sun would have already exhausted the story before the body was laid to earth.
For his part, Coward himself danced lightly round the subject, never confirming, never denying. It may have lent a reflected glamour (not that Coward needed it, but he was one of the great 20th century snobs, and a social climber to rival even that egregious social-climber, Cecil Beaton), but it also bespoke a certain dignity. Contrast that with the exposes of the modern world of Hello! or the News of the World, or, indeed, of Margaret Cook and William Jefferson Clinton.
Writing in The New York Times on 10 January this year, journalist Ariel Swartley noted: "In our current culture of revelation, it strikes us as a shame that for all his logorrhea, Coward never quite came out and said what he meant, or who he was. That privacy cost him love, and the energy he invested in maintaining his front made him more callous than he might have been to those less amusing than him, including people of other races and financial strata.
"And yet he broke through language barriers we've forgotten ever existed." In a classless country like America, that might be true: perhaps part of Coward's appeal - and that of his stiff upper lip - to his countrymen is that we haven't.
As the century slips away and uncertainty looms, Coward's reassuring, reticent world is increasingly appealing: a lost world in which one is not defined by one's sexual exploits or ability to externalise emotion; in which one could be oneself, without recourse to self-exposure. Yes, it was a time of certain prejudices which we are well rid of; but have we really gained that much?
Philip Hoare's biography of Noel Coward is published by Random House