Havergal Brian's `The Cenci' QEH, SBC, London
On 9 September next year it will be 400 years to the day since the brutal murder of one of the nastiest characters in history. That was when, according to the 18th-century Italian historian Ludovico Muratori, two hired assassins drove a nail through the brain of Count Francesco Cenci. And this year sees the 25th anniversary of the death - at the grand age of 96 and in rather less dramatic circumstances - of the English composer Havergal Brian, the third of whose five operas, The Cenci, was given its world premiere last Friday evening in a concert performance mounted by the Havergal Brian Society in commemoration of the second of those two anniversaries.

The Cenci is Shelley's account of the ghastly but true history of how the corrupt and depraved Count Cenci systematically abused and eventually raped his daughter Beatrice, who then arranged her father's murder and, along with her step-mother Lucrezia and brother Giacomo, was executed by order of the Pope.

Brian was 75 when, in 1951, he sat down to compose The Cenci, excising large parts of Shelley's five-act drama to bring it down to eight compact scenes but losing none of its primal horror. Last Friday's premiere revealed it to be a masterpiece - an unorthodox one, perhaps, and not without its problems, but none the less of unarguable and immediate power.

The work opens with an extensive Preludio tragico, flecked with unexpected humour and brief evocations of courtly dance that suggest a world lost to the characters about to be presented. Brian's writing for the orchestra is as natural as Chopin's for the piano, and draws on an extraordinarily inventive palette of unexpected instrumental combinations.

The elliptical style is that of the late Brian symphonies that are becoming better known in Marco Polo's on-going CD series: an entirely individual amalgam of a big-hearted English bonhomie that harks back to Elgar; and a much harder-edged astringent flavour that suggests Brian was fully aware of the most recent developments around him. Its dark, bass-heavy quality suits Shelley's Gothic atmosphere perfectly, with long-legged writing for the brass and lower strings - and there cannot be another opera with such a grateful part for tuba.

The declamatory nature of Brian's word-setting gives The Cenci a kind of hieratic, epic dignity that belies its gruesome subject. One of the problems that affected the premiere - the tendency of the orchestra to drown vocal lines - would largely be solved in a staged presentation, with the soloists better able to project above the orchestral wash. Another is less easily overcome: Brian intermittently asks his characters to get through an unrealistic amount of text in the time he leaves available, with the result that Shelley's image-laden lines sometimes go for nothing. That said, it worked: this was a very real dramatic experience of unusual intensity.

David Wilson-Johnson brought the evil Count to unnerving life, and Helen Field found the right blend of gentleness and steel in Beatrice; Inga Jonsdottir was a dignified Lucrezia and Stuart Kale a compelling Cardinal Camillo, with Nicholas Buxton, Jeffrey Carl and Justin Lavender all outstanding in a series of subsidiary roles.

The conductor of the Millennium Sinfonia was James Kelleher, a Bernstein protege. Brian's idiom is not an easy one to master, but in these hands it seemed as natural as eating beef off the bone. First performances this convincing are rare indeed.

The Cenci has waited nearly half a century to be heard. It now cries out to be staged.