But, whatever you do, don't mention the classic hit single, one of the 20 most-played tunes of all time, to Harley. Although "that song" - he almost spits out the words - has made him rich beyond his wildest dreams, he hates being seen as a one-hit wonder. Even worse, he hates lazy journalists rehashing the obligatory "What ever happened to?" features whenever "Make Me Smile" - whoops, I mentioned it - is rediscovered by a new generation of glammed-up glitterati.
"Look, I loathe being referred to as a Seventies rock star and being talked about in the past tense," he warns. "If someone says I was their idol - that's no good to me. The person they're talking about is a former incarnation."
It is true that, in a previous life, he was a hell-raising, drug-taking, wild-oats-sowing Mr Soft (the title of an earlier, not-so-classic hit single). But, to the residents of a quiet village on the Essex-Suffolk border, he is the family-loving, God-fearing, Bible-preaching Mr Nice (his real name). For many years the villagers didn't realise, or didn't let on, that the intense, middle-aged chap who read the lesson every week was Big In The Seventies, which suited him down to the ground; being "a very private man" he relished the anonymity.
Balding, bespectacled, afflicted by a limp - the legacy of a childhood polio attack - he remains fiercely protective of his personal space. At one point in the interview the doorbell rings. "What fresh hell is this?" he groans, recalling the time an elderly gentleman called to say he'd heard Mr Nice had some connection with the music business, and would he mind listening to a tape his grandson had made? "I said, 'Yes. Yes I most certainly would mind'."
The one-time Cockney Rebel eventually outed himself at a church committee meeting. "I told this chap I was a rock musician." He smiles wickedly. "And that if it can be grown in a field or a laboratory, I've done it. I don't any more, of course. But I've lived quite dangerously." Every so often he gets the rock-star itch, picks up his guitar and goes out gigging, just like the old days. Mind you, he's careful to keep "that song" back until the encore. "If it came any earlier, people would leave. Sometimes I think it is all they've come to hear."
While less hip than contemporaries such as Bowie and Ferry, Harley's legacy is arguably as great, especially among Britpop bands such as Suede and Blur. His cavalier approach to PR probably sealed his fate as, in Tony Parsons' words, "glitter's forgotten boy".
"These reporters - hah! - would all think they were bigger than me. I used to ask them if they had ever taken shorthand notes at court, or doorstepped. Naturally, they hadn't."
Such withering, and ultimately career-imploding, contempt for a profession he once graced (in an even earlier incarnation, he worked on local papers in Essex and London) earned him a reputation for being prickly and arrogant. But the self-destruct button was fatally pressed when, at the height of his fame in the late Seventies, he went AWOL on a sex-and-drugs binge in America. I suddenly find myself humming, out of his earshot, "You had it all, and threw it all away".
But it is another great Cockney Rebel line that comes to mind as he agonises about "conflicting lifestyles" in the well-furnished sitting room of his beautiful Georgian home: "It's like a mild schizophrenia." Once on the road, admits the devoutly religious Mr Nice, 47, he soon reverts to the Mr Soft persona which bewitched boa-wearers and panicked moral guardians all those years ago.
These days he is a born-again moralist who pours scorn on "the hypocrites who use the church for weddings and christenings but never attend for the rest of the year". At the same time he gets a fantastic adrenaline rush from "the biz", guiltily basking in the fans' adoration. He fears he will never resolve this Jekyll-and-Hyde dichotomy. "I am a born leader, a motivator; it's just a natural part of my character. I enjoy the limelight and feel like I was destined to be on a big stage. I don't tour for four years, then I go into overdrive and I can't stop. I just love touring."
Although he sees it as a millstone, it is surely only the enduring appeal of "Make Me Smile" that allows him to keep on touring. Which is fair enough, given that it's one of the best pop songs of all time, a classic as instantly recognisable as "Yesterday" and "My Way". "Not best," he growls. "Most- played, maybe. I'm sorry to be pedantic, but 'best' is entirely subjective."
Steve Harley plays Cambridge Corn Exchange on 8 March (01223 357851 for tickets and details).