Brighton's local newspaper, The Argus, reports that Wordsworth told the audience he "did not believe in" Gant's piece, later adding that it was a matter of artistic integrity.
Irked tickets holders, many of whom had come especially for the premiere, were refunded their money.
Orchestra manager Ivan Rockey pointed out, however, that not everyone received, or requested, a refund — because "there was a large proportion of the audience who rather liked the change of program."
The Gant work was replaced with an (unspecified) Mendelssohn piece.
Ticket holder Lynn Riley told the paper, "It was professional incompetence on the part of the conductor. He had had the music since November and should have known what the music was going to sound like and he waited until just before the performance to say something which caused a lot of people a lot of expense. If he was right that the music was rubbish he should have said so earlier. And if he is wrong he has castigated a first-class composer and his music."
Gant has been organist, choirmaster and composer at the Queen's Chapel Royal since 2000. He was a choral scholar at St. John's College, Cambridge and subsequently sang with the Tallis Scholars, the Sixteen, the Monteverdi Choir and the Cambridge Singers.
He also studied composition at the Royal Academy of Music with Paul Patterson and won two of the Academy's composition prizes. In 2002, he was awarded a PhD in composition and contemporary music from Goldsmith's College, University of London, where he studied with Sadie Harrison.
Wordsworth, in addition to being the principal conductor of the Brighton Philharmonic, is the Conductor Laureate of the BBC Concert Orchestra, of which he was chief conductor from 1989 to 2006.