It’s not every day that one goes to a dinner party at lunchtime, but this was a rather special dinner party – A Dinner Party for John Cage. It formed the centerpiece of a lunchtime “happening” at St John’s Smith Square to celebrate the 70th birthday of American-British composer Stephen Montague.

“Take a seat, or wander around, if you like” the composer himself invited us as we entered the elegant concert space of St John’s. “Or try the toy piano!” As he spoke, the tinkling of the toy piano reached our ears while we turned our gaze to the table set for dinner in the middle of the hall, around which fourteen people, all in dinner dress, were seated. Each one wore a sparkly party hat, but our attention was immediately drawn to the girl in the turquoise corset and the giant orange dragon on her head...

Stephen Montague created A Dinner Party for John Cage in 2012, as part of the Musicircus, which he directed at ENO last year to mark Cage’s 100th anniversary. Montague worked with Cage on many occasions and made some of his first recordings of works for prepared piano for the BBC. His interest in and close relationship with Cage, his philosophy and aesthetics, and sense of humour, is evident in the Dinner Party, which, like Cage’s iconic and iconoclastic 4’33” challenges traditional notions of what constitutes “music”. The “diners” (students from the Trinity Laban Conservatoire of Music & Dance students, English National Opera Works singers, and two freelance singers) chattered and hummed, sang, rattled their cutlery against their plates, tapped the table with chopsticks, and even “played” their wine glasses, in a fair imitation of a glass harmonica. Occasionally, they would break into recognisable songs: close harmony renditions of Greensleeves, Clementine or When Johnny Comes Marching Home, or snatches of opera. Just like at a proper dinner party, the noise of the diners ebbed and flowed, garrulous and rowdy, or quiet and thoughtful. The dinner party seemed random, but in fact, like the other performances during the event, it was based on a “menu” of options and time frames, and a performance created through chance operations (the roll of a dice).

While the dinner party progressed, a string orchestra in the balcony performed Montague’s atmospheric Snowscape, inspired by snowfall on an empty landscape. From the organ came high-pitched squeaks and clusters of sound, flutings and shimmers high in the register. Meanwhile, on the stage, three pianists (Margaret Leng Tan, Philip Mead and Jessica Zhu) played works from Montague’s collection Autumn Leaves, the selection of pieces, and performer, also dependent on the simple roll of a dice. There was even the world première of Montague’s new work Insectus.

As the musicians played, the composer wandered around the hall, occasionally pausing to talk to friends or colleagues, seeming to subtly “direct” the proceedings. In fact, the only aspect of the concert which was stage-managed was the timing: as the composer explained to me afterwards, the musicians and performers were synchronized with one another by means of atomic clocks, to ensure that each element of the concert started and ended at exactly the same time. Whatever happened in between was down to chance. At times the piano music seemed like background music to the dinner party; at other times, it was a formal performance, commanding our full attention.

An event, a “happening”, such as this invites audience participation, and many people embraced the experience from the outset, drifting around the hall, taking photographs, talking to friends. Others seemed quite bemused, unsure what was expected of them as audience members, and how the event would unfold. Close to where we were sitting, a couple talked quite loudly, perhaps covering their anxiety about how they should behave. This was a clever, but possibly unintentional, device on the part of the composer, who like Cage, was playing with the formal etiquette of the concert hall and challenging the audience’s expectations. As people settled into the event, the dynamic in the hall shifted and settled. Some people sat on the stage, with the pianists, others wandered around the hall. Occasionally, the toy piano’s distinctive jingling voice was heard beyond the hubbub of the dinner party.

Just before 2pm, the diners hushed, and the composer stepped forward and led the applause, signalling that the event was over.

As concerts go, this was definitely the most unusual, challenging and amusing of musical experiences, as one would expect from one of the most distinctive composers working today.