YOU have to admire a composer and librettist prepared to suffer for their art, especially if they are writing about a martyr who himself suffered a horrible death. So before a note was sounded there was plenty of goodwill towards Stephen Barlow and Philip Wells, who trudged the pilgrim route from London to Canterbury last October — sponsored by hundreds of wellwishers — to raise the necessary funding for King, their new opera about St Thomas à Becket.

On the whole it was shoe leather well spent. Staged simply but atmospherically by Harry Silverstein in the soaring nave of Canterbury Cathedral, just yards from the spot where the “turbulent priest” was butchered by Henry II’s hotheaded henchmen, King emerges as a sincere and intelligent retelling of this quintessential conflict between Church and State, expedience and conscience, and different sorts of love and duty.

Action-packed it ain’t. But compared with T. S. Eliot’s gloomy Murder in the Cathedral it fair whizzes along. And it is ingeniously conceived, visually and especially aurally, for the vast, echoing space in which it is sited.

The beginning is inspired. In the distance the cathedral choir intones the setting of Vespers that à Becket would have heard on that fatal December afternoon in 1170. The four knights rush up the steps towards the choir. Cassocked choristers run out in disarray. There is the ominous clash of sword against stone, a chilling clarinet shriek, a tolling bell, sombre organ chords — and the opera has started.

The events leading up to the murder are then recalled in eight scenes linked by a modern-day narrator (Wells himself, speaking his well-honed lines with model clarity) and six children, whose questions trigger each new tableau.

This is a clever framing device, though rather weakened when the opera ends abruptly before its intended epilogue (which is nevertheless printed in the programme). Lack of preparation time? It certainly feels unfinished.

Elsewhere, however, there is much to admire. Barlow’s music, reminiscent of late Britten, is crafted for a chamber ensemble prominently featuring a harp and an Indian tabla drum. It includes a striking passage of spoken choral declamation and some poignantly lyrical solos for Queen Eleanor, radiantly sung by Kate Ladner.

Nicholas Folwell offers a wry cameo as the Bishop of London, amusingly forced to clip his monarch’s toenails. But the bulk of the drama is carried by Philip Joll as the noble, anguished à Becket and Robert Burt as the volatile Henry. Both are outstanding.

It’s hard to imagine King staged anywhere except Canterbury. But I hope that it won’t now vanish without trace.