Lange, of course, was easily persuaded to give us her Blanche. Sykes, offered a small but shapely role as Arnolphe's servant Alain, was less willingly seduced by the Hall of fame. "I was loath to get into this classical form,'' he says, "because I've always been a vaudeville man. I'd met Peter Hall once before, 20 years ago in a make-up room in Canada, when we were both appearing on the same chat show. When I met him again last year, he said: `Moliere had a great affinity to vaudeville artists. You probably are the last remaining top-of-the-bill vaudeville man: you're ideal casting for this.' I thought, he knows what he's talking about, yes I'll do it.''
Sykes still wasn't entirely sure what 17th-century French farce entailed. The text called loosely for comedy routines, so he duly submitted a few ideas to Hall, who said, "Brilliant, brilliant. I'll just give them to Ranjit." Ranjit Bolt, Sykes discovered, was Hall's verse translator, hired to mould his gags into rhyme. A period of negotiation ensued in which Sykes explained to Hall that "when you translate a vaudeville man into verse, you emasculate him. He's got to go on that stage and sound as if he's thought of it that moment. And if it's in verse he obviously hasn't, so you've taken away some of his attack.'' He argued, rather cunningly, that Moliere's vaudevillians "were probably illiterate vagabonds. He would have said to them, `Give me three minutes of that routine I saw you doing at the teatro in Madrid.' And not only that: they probably would have gone off-stage doing backflips.''
This is one of the few vaudevillean party tricks beyond Sykes's reach. Never mind that he's totally deaf and largely blind, he can still do a pacy hat routine, a nifty little sight gag about the treachery of the stage revolve, and generally hold the audience in the palm of his hand with organic, largely wordless comedy. At the first preview, he closed the hat routine by mimicking a gunslinger firing his weapon, then twirling it round his finger as he returns it to an imaginary holster. It turns out it was freshly minted that night, and the next morning when we meet he is glad of the reassurance that it came off.
Sykes had his first ear operation in 1952, and another a decade later, since when he has worn a hearing-aid camouflaged as a pair of thick-rimmed glasses. He sometimes rubs his eyes through the place where the lenses would be: a sight gag if there was one. The arms of the glasses have micro- speakers that conduct sound through his skull. (Apparently he has "good bone conduction'', which sounds like something all comics should have.) What it can't do is give the noise a co-ordinate. "I could sit in a restaurant looking at my plate and I'd be laughing - when there's a chuckle I always chuckle too, so they think I can hear what's going on - and I'd look up and there'd be stony faces round the table, and I'd realise it was a joke being told three tables away. They're all looking at me thinking, `Aah, he's thinking of something funny.' ''
We're in Sykes's office, a spacious first-floor room down a Bayswater backstreet. All the greats have mingled here, and most of them still line the walls. His favourite photograph finds him deep in conversation with the Queen. He hasn't got his glasses on, and can't hear a word she's saying. It's somehow fitting that among Sykes's most garlanded works is The Plank, a silent film by someone who couldn't have a deeper affinity with silence. More than most comics of his generation, he was always a virtuoso of the visual. "I believe that one visual joke is worth a page of dialogue.''
It was all the crueller, then, that his eyes packed up on him in his mid-sixties (he is 73 now). He has blurred peripheral vision, and can see shapes only out of the corner of his eye. He looks over your shoulder when addressing you. "If I look straight at you there's just a black nothing. The doctor told me it was a common affliction in the elderly. I said, `I don't know what it's got to do with me then.' '' There's also the odd memory lapse: he has to ring down to his secretary Janet ("the eyes and ears of the world downstairs'') for the names of one or two recent co- stars.
But he seems chipper in rollneck and smart check jacket, no doubt buoyed by what he'd be reluctant to describe as a comeback. The West End run ahead is his first for seven years, the BBC recently repeated some of the long-running sitcom Sykes, and The Great Crime of Grapplewick, one of the unfilmed movie scripts he's ecologically recycling as fiction, was published in the autumn. (The planned film would have starred Tony Hancock and Terry-Thomas). So he is by no means the embittered comic pensioner railing against modern comedy, as portrayed recently in the Times. "Do I look bitter? It takes years to be bitter, and I don't have the time. You've got to sit there with a rug over your knee and really work at it. I don't want to be seen as some sort of Jeremiah.'' He won't deny that some younger comedians aren't his cup of tea. It's telling that his favourite comic is Victoria Wood, whose long off-screen apprenticeship most closely resembled the old-fashioned method of learning the ropes. He also likes Rory Bremner. What about the neo-traditionalist Harry Enfield? "I can't comment on Harry Enfield, because to be quite honest I've never seen him.''
Sykes's simple theory of comedy is that it should come from the heart rather than the head, and that good comedy is medicinal. "One show of Ken Dodd's is worth six months on the National Health. The great comics all had one thing in common, and that was vulnerability. It seems to me that a lot of today's comedy is fireproof. People shouting at each other. Well, children do that."
If he's not quite regarded as one of the greats, it's because he was always as much a writer as a performer, a split ability that in his time was surprisingly rare. He's much more of a household name than Ray Galton and Alan Simpson (Steptoe and Son, Hancock's Half Hour), the great comic writers of their generation, but not quite up there with Frankie Howerd, Tommy Cooper, The Goons, Norman Wisdom and Hancock, for all of whom he wrote. Perhaps it's because of this that he's been spared the great comedian's traditional penalty, the off-stage misery. Actually, he thinks the dichotomy between genius and glumness is exaggerated. "People call it a dark side, but all the comedians I've ever known are always thinking every waking hour. You might be on the verge of cracking the funniest routine, but you've got such a serious expression people think, `What a miserable sod he is.' A better word could be `anxious'. I've very rarely seen a feed with lines on his face. All the lines are on the face of the comic. Ernie has a lovely baby face. Eric was always staring morosely at the floor.''
His own worry lines started appearing very promptly. His mother died giving birth to him. His father remarried, "and I was left to my own thoughts. I always felt like a lodger in my own house; I had a lot of time to live within my own head. I didn't have anybody to run to bury my head in when I was in trouble. There is a price to pay for everything. But I find that the price is very, very reasonable".
`The School For Wives' opens tomorrow at the Piccadilly Theatre, London, W1 (0171-369 1734); `The Great Crime of Grapplewick' is published by Virgin at pounds 9.99