Anyone expecting an evening of soul bearing will have been disappointed. In the hands of musical theatre's resident renaissance man Jeremy Sands, who will direct Sondheim's latest work, Passion, next spring, the conversation was relaxed and genial. But Sondheim is famous for giving little away about the well springs of his work, let alone the personal motivations behind his creative life.
His sole British newspaper interview revealed, a trifle coyly, that, "he has never been married or had a known long-term partner", and that, it seems, is that.
He regards his work and life as being entirely separate, even denying that Into the Woods (1986), in which indiscriminate death is visited upon an entire community, has anything to do with Aids. This from a New Yorker who doubtless spent too much of the 1980s attending funerals.
What the talk made clear was the collaborative nature of musicals and, for the huge mix of earnest young composers, directors and good old-fashioned fans who packed the auditorium, that was plenty to be getting on with.
As far back as 1957, following the success of West Side Story for which Sondheim supplied the lyrics, he and Hal Prince decided to do a romantic comedy. They tried to get the rights to Anouilh's "truly sour, mean play" Ring Around the Moon, but were told, "Only if Leonard Bernstein does the music".
He remained attracted to the idea of combining "lightness of texture with sharpness of attack" in a work which obeyed the dramatic unities of time, manner and place, and after another failed attempt several years later to secure the Anouilh they opted for Bergman's exquisitely dark romantic comedy Smiles of the Summer Night.
Sondheim observes that every time he hears the score or watches the show, "I expect not to like it, but I do." This is good news for the current production, which he has been working on with its director Sean Mathias, a first-timer in the genre. Yet, with several previews and rehearsals still to go, he remained tantalisingly silent on that subject.
He chatted happily about his and the show's big hit "Send in the Clowns", written during rehearsals expressly for the short-breathed Glynis Johns, and wisely dismissed the film, which featured Liz Taylor's version of the song assembled from a sea of separate edits.
His tale of coming up with the grand full-company finale "A Weekend in the Country" late in the day made everyone wonder just what he had actually written before they began.
"Why do they have to have him sitting in a hospital room?" remarked one audience member to a friend. It was not deliberate. The stage was set for a performance of What the Butler Saw. With Orton's emphasis on language, artifice and, above all, irony it was, however, deliciously appropriate.
n `A Little Night Music' opens at the Olivier tomorrow. Booking: 0171- 928 2252