Louise Brooks was an American film actress with extraordinary sexual charisma. In 1929, she starred in two films by the German director George W Pabst - Diary of a Lost Girl and Pandora's Box, based on Wedekind's Lulu plays - after which she returned to America, where her career went into steady decline.

Until, that is, the late 1970s, when her path crossed that of the legendary Kenneth Tynan who, for three decades, reigned supreme on both sides of the Atlantic as the sharpest, most controversial and wittiest theatre critic of his generation. The British Tynan harboured lifelong erotic fantasies of Brooks and her amoral Lulu. In 1978, he spent several days alone with the then ageing and ailing actress at her New York apartment, in order to gather material for an article that was to launch Brooks once again into the limelight after decades of anonymity. The resulting article in The New Yorker magazine (June 1979) was considered one of Tynan's best-ever profiles.

An inveterate smoker and ridden with emphysema, Tynan died in 1980; Brooks died five years later, in 1985. Speculation about what happened during the pair's real-life meeting is the inspiration for Janet Munsil's acclaimed play, Smoking with Lulu, which is currently playing at London's Soho Theatre, starring Thelma Barlow.

But what did Tynan really think about the screen siren? The Diaries of Kenneth Tynan - edited by John Lahr and published by Bloomsbury - reveal the critic's most indiscreet thoughts on Brooks and myriad other matters during his 1970s heyday.

30 June 1972

Two great beauties on two successive nights: yesterday, Louise Brooks in Pabst's Pandora's Box on TV. Eton-cropped, with a fringe swirled forward at earlobe height and a face open to any sexual suggestion, candid and mischievous, full of delight and magnetism; the prototype of Sally Bowles. Is her broad-necked bisexuality part of the attraction? At all events: Loulse B is unarmoured, in the Reichian sense of the word. (A sense which, since reading Reich, I find indispensable in everyday conversation.)

The second beauty: Natalia Makarova, the defector from the Kirov Ballet, tonight seen with the Royal Ballet for the first time in Swan Lake. If all ballet were like this performance, I would find this vulgar Victorian after-dinner entertainment defensible. As Odette (Electra forbidden to fuck her father), she really is a bird, quivering and volatile; in the second act she glows, infinitely vulnerable because capable of surrender. As Odile in Act III, she glitters: the bird becomes a snake; sinuous within its flexible armour. From the waist upwards, she is the greatest female dancer I have ever seen; the wave-like motions of her arms, the arc of her neck, are not forgettable. Whenever she leaves the stage, and the corps de ballet appears, you unfairly think: Who are these elephants? She has high cheekbones and predatory teeth and will doubtless keep this threadbare and spendthrift pseudo-art - eked out by the nostalgia of poor artists and the arrivisme of snobs - alive for a few years longer than it deserves.

5 July 1972

In my office at the NT the house phone rings and it's Peter Hall popping in for a friendly but fairly definitive chat. He pays extravagant but (I think) sincere tribute to my part in creating the NT and adds (not 'but' adds - he is too much the diplomat even to imply 'but') that he hopes I don't envisage that I'm to be thrown out. Nevertheless, he's not entirely sure (and wants my views on) whether we shall get on, both being so good at politicking, both with such strong ideas. I disabuse him of the thought that I ever intended (even under Michael Blakemore) to stay on after the move to the new building, when I would like to be phased out. I sense he is privately relieved, though not surprised.

8 January 1978

A sad and rainy Christmas. In the following week, I finish my Carson piece - around 25,000 words - while bank account dwindles to under-zero and (due to an accounting error committed by my secretary) cheques begin to bounce. After a week of suspense, Mr Shawn calls. He thinks the piece 'stunning' and 'marvellous' and promises an immediate cheque to tide me over. It arrives ($15,000).

A recent TV showing of Pandora's Box brings back all my infatuation for Miss B - she runs through my life like a magnetic threat, this shameless urchin tomboy, this unbroken, breakable porcelain colt, this prairie princess, equally at home in a slum pub or the royal suite at Neuschwaustein, creature of impulse, unpretentious temptress capable of dissolving into a fit of the giggles at a romantic climax, amoral but selfless, lesbian and hetero, with that sleek black cloche of hair that rings so many bells in my memory - Eton-cropped at the back with heavy fringe and kiss-curls bracketing the cheekbones - the only star actress I can imagine either being enslaved to or wanting to enslave.

Wake before dawn having dreamed all night of words. Why do all words that juxtapose the letters B and L (in that order) have connotations of clownish clumsiness? 'Bl' people dribble when they drink; their stomachs rumble after meals which they gobble. Rather than walk, they amble, stumble, hobble, shamble, or tumble; they are bloated and bleary-eyed; vocally they babble, bleat, burble, bluster, and mumble; physically, they are feeble. In the Pall Mall area, they are Blimpish blighters; en masse, they are a rabble, always grumbling and in trouble. They fumble every task, and their lives are a jumble. If black, they have the blues. If women, they are blowsy, their minds are a blank, and rapidly crumble. At school they are blockheads who scatter their pages with blots. Their skin is blemished, covered in blotches and blackheads. They are blinkered against reality and unable to prevent their thoughts from rambling, they merely babble. Many of them are Russian: Oblomov is the classic example (though some, like Leopold Bloom, are Irish and expert in blarney), terribly short of rubles. In a word, they are bumblers. Yet they are harmless blokes, for the most part humble, and although impossible to live with, they shall in good time be blessed. (In many ways, I am their double.)

May 1978

I have not written about the events of this devastating summer - the most turbulent and shattering period of my life. I do not propose to relive it, even in words. In May I spent four happy days in Rochester, NY with Louise Brooks, who was a joy - bedridden but birdlike, hilariously indiscreet (she claims that when she masturbates, even at 71 - 'I sit on that couch and the spurt from my cunt goes Poww! clear across to that record player on the other side of the room. That's five and a quarter yards!'), together with detailed stones of her affairs with (Charlie) Chaplin, (William Randolph) Hearst, (George) Pabst (!) etc.

The above are edited excerpts from The Diaries of Kenneth Tynan, published by Bloomsbury in hardback (priced £25.00) and on talking-book cassette (£9.99). For more information or to order either, please visit the Bloomsbury website.

Click here to win one of ten copies of the diaries on cassette, read by Simon Callow.

Smoking with Lulu continues at London's Soho Theatre until 30 March 2002.