Just then a great heave of high-cultured, high-toned people - publishers, poets, poetasters, representatives of The Times, The Times Literary Supplement - sweep me down and into my seat none too delicately.
It's hot and full down there in the stalls, and quite a few people are already straining their eyes to read from the same book (well, different copies of the same book): Opened Ground by Seamus Heaney, his collected poems of 30 years that he's here to read from. Seamus will be amongst us, fully rested, in a moment or two. Meanwhile, we admire the set for Major Barbara against which the cattle-dealer's son will be obliged to read, a highly respectable drawing room scene - and there's his lectern, a funny, spindly, gothic thing, plonked down on the edge of the carpet.
A tall, thin, nervy Waterstone's type skips on next to remind us that Seamus is a man of huge significance, and indeed one of the greats of world literature, and that all proceeds of the evening will be going to the Medical Foundation in support of their work amongst victims of torture throughout the world.
Then on he strides, the hugely significant man himself, broad of shoulder, square and ruddy of face, hair, brilliantly white as bleached, flattened straw, combed forward to conceal a lack. This reading will be longer than the usual poetry reading, he tells us as he squares up the book on the lectern. After all, the event is associated with victims of torture. That quip gets an awkward guffaw or two, and then it's on to the poems, one from each of his books, from 1966 onwards.
The marvel of an evening with Heaney is that every word that he reads - and each one comes out slow and measured - is singled out for our particular attention, as if held up in the air to be judged and weighed by the voice that's speaking it, and then, with great and solemn care, handed over to the listener. And between every poem there is the commentary, the amusing aside, the scrupulous and incisive link between one poem and another, knitting the snippet of biography to the poetic act.
From the middle 1970s, for example, he reads us "A Constable Calls", which describes a familiar childhood experience of seeing a member of the Royal Ulster Constabulary arriving on his bicycle at his father's farm to check the tillage returns. "I remember that baton of his," says Heaney, "so beautifully stitched..." He steps aside from the lectern and mimics that act of precision-stitching in the air with his fingers. "It was so fascinating and so scaresome - especially if you were called Seamus. Not so perhaps if you were a William. The problem was that my father was so inaccurate in his recollections of what was being grown on the farm. That terrified me..."
Heaney and his audience at the Piccadilly belong to the world of Radio Three. The novelist Iain Banks, who read at the British Library one rainy evening last week, writes to the accompaniment of Radio One, and his audience is much more varied, much less self-consciously literary - there was the half-drowned kid in the baseball cap, for example, who bounced in on the balls of his feet and a couple of guys examining spread sheets on the front row. Could they be analysing some of his more fantastical plots?
Heaney has a single volume of fewer than 500 pages to show for a lifetime's endeavours as a poet. The feverishly prolific Banks writes one novel a year and has been doing so since The Wasp Factory was published in 1984. Heaney lives in perpetual fear that the gift of poetry will depart from him all of a sudden, and that he will be left with the cold comfort of silence. "Every poet is in a panic that it will stop," he told his audience. "You may be walking over the cliff at any moment." Listening to Iain Banks makes such a thought seem unimaginable. He just can't seem to stop the ideas coming.
Banks begins with a reading from A Song of Stone, his latest. Being this year's it must be what his publishers describe as "mainstream" rather than science fiction. He tends to alternate between the two.
He doesn't read too well. He seems all charged up, in too much of a hurry. Perhaps he's working out the plot of the next one as he reads this one. He stands just a little too far from the microphone as well, so that the occasional crucial link word is lost and all sense collapses in a heap.
Here is the gist of the story: there's been a break-down of society in the middle ages. The female lieutenant of a band of brigands is holed- up in a castle somewhere in the middle of nowhere - or perhaps I just foolishly just missed the name. It's the usual sort of 400-year-old castle - complete with gloomy paintings, tapestries - the sort of place where you habitually enquire after ghosts. She does. She's smart, dangerous, thin-lipped and sassy, this lieut, with cold grey coals for eyes. She uses her cutlery with deadly dexterity. She taunts people. She yawns a lot. (Banks tells us afterwards that he likes strong women who don't take too much shit from men). Her companions are all called by their nicknames - so that they can re-invent themselves effortlessly like medieval existentialists. Here are some of their names: Death-Wish, Victim, Karmer, Love-God, Half- Cast, Fender... Fender? Could that be the microphone again?
The audience doesn't seem to mind too much. The crucial fact is that this Fifeshire phenomenon of amazing novelistic productivity is with us.
Then Banks stops, and walks away from the microphone. He's much younger, nervier and faster moving than Heaney. He stands in the centre of the stage, shifting from foot to foot. He clips a tiny mike to his shirt because he's not fond of staying still when he's beating off eager questions, he tells us, pulling a funny face and giggling.
After listening carefully to a couple of moments of intolerable silence, he shakes his head of tousled curls, grins with all his teeth and says, as if to remind all we wet dolts of our roles here: "Now you're going to be asking a lot of deeply penetrating questions, and getting a lot of shite in return..."
Seamus Heaney lolls against the gothic lectern of the Piccadilly Theatre, waiting for the next question.
"What's your favourite colour?" shouts a female voice from the Gods. He squints up, disbelieving.
"Green," he replies.