When the modern history of artistic collaborations gets written, the chapter on words and music will need to give some space to George Mackay Brown and Peter Maxwell Davies who, over the past 20 years, have made a poet-and- composer partnership less glamorous than Hoffmansthal and Strauss, less dazzling than Auden and Britten, but of stature and - from all the indications - durability. Blown together by the winds and tides and sense of place of Orkney, where Brown was born and Davies (an adopted Scot) made his home from the early Seventies, they generated a body of work which seems to have been carved, verbally and musically, out of the landscape: hard- grained, massive and austere, but dreaming dreams of the ancient past which Brown (preoccupied with Nordic and early Christian mythic history) and Davies (compositionally steeped in plainsong) brandished like an amulet against everything they didn't care for in the 20th century.

For two decades they were also the genii loci of the St Magnus Festival in Orkney, a sort of Aldeburgh of the north where the fortuitous residence of two prominent creative artists attracted serious names to come and work in a place (and in venues) they wouldn't otherwise have contemplated. But earlier this year Mackay Brown died - on the very day that Maxwell Davies completed his 6th Symphony. Last weekend, in the opening orchestral concert of the 1996 St Magnus Festival, the symphony had its world premiere - played by the Royal Philharmonic Orchestra in the barely contemplateable venue of the Phoenix Cinema, Kirkwall (apparently the only place in Orkney large enough), and dedicated to Mackay Brown's memory.

The memorial tag on this new symphony has, of course, been applied retroactively; and although it isn't inappropriate to the mood of statuesque melancholy that colours the score from the outset, there is no programme here, memorial or otherwise. What you hear follows the grand tradition of abstract symphonic writing to which Davies has probably made a more significant contribution than any composer alive during the past two decades. But all six of his designated symphonies have been Orkney scores and in some way - emotional, structural, lyrical - a response to landscape. Introducing Symphony No 6 in Kirkwall Town Hall before the premiere, Davies said he thought he should be giving a pre-performance walk rather than talk; and it isn't hard to hear the sounds of Orcadian life filtering through the textures of the piece, at all levels from the epic scale of tidal movement to the mundane folksiness of the Scotch snap - a rhythmic feature which has become tiresomely prevalent in Davies's writing.

In one respect, though, No 6 breaks (or maybe, recasts) the mould of the previous symphonies. Until now, they seemed to be retracting in dimension: making (as Davies likes to say) the notes work harder for their keep. No 5 had a duration of only 26 minutes; No 6 lasts nearly 50. But it effectively absorbs into its own span the reductivist drive, with three movements that progressively pare down the density of texture and - as Davies would have it - reveal an inner stratum of material which has been present from the start, but hidden. As with previous scores, the organisation depends not only on vertical divisions - intercutting periods of static exposition and active development - but on lateral layering that creates a semblance of perspective depth: a sense of separate but superimposed musical domains, foreground and background, with the gradual revelation of the background as the music's quest.

I have to say that on one hearing in the Phoenix, with its stifling, dead acoustic, it was hard to sort out what was going on. We'll have to wait until the symphony comes down to the Proms on 6 August for that. But one hearing was enough to know it as writing of integrity and stature; and not just a co-opted memorial to Mackay Brown but a tribute to the RPO, with an abundance of soloistic passages that sometimes steer the music close to the spirit of a concerto for orchestra. Conventional symphonic form, needless to add, doesn't figure in the equation.

Davies has a special relationship with the beleaguered RPO - he threatened to resign his knighthood in its defence a couple of years ago - and having gone to the trouble of airlifting the orchestra to Orkney for the symphony he put it to work on a few of his other scores: A Spell for Green Corn (part of the increasing catalogue of Maxwell Davies in Radio 2 mode), and Time and the Raven (a not so successful occasional piece, tailored to a political agenda but half-hearted about it). There were also performances of the 2nd Beethoven Piano Concerto and the Sibelius Violin Concerto, all conducted by Davies himself. And that was the problem. Davies has been conducting off and on since the old days of the Fires of London, and brings the insights of a powerful creative mind to the task - conscientiously and selflessly, in total service to the music. But his hand technique (he doesn't use a stick) is weak, he doesn't lead commandingly; and the Beethoven was pretty undistinguished, with a soloist - Joanna MacGregor - whose animal instinct as a troubleshooter, sorting out the complexities of new works, can be exhilarating but doesn't as yet come with the necessary polish for core repertory.

The best playing I heard in Orkney was from Tasmin Little, who made a heroic soloist in trying circumstances for the Sibelius, and also gave a recital in Kirkwall's compactly handsome St Magnus Cathedral that was pure joy. With a big, muscular tone and massive personality, she confounds the old orchestral prejudice against women string players on the ground that they can't sustain weighted sound. With the support of her fine accompanist, John Lenehan, Ms Little sustained a meaty, almost overloaded programme; and it got the ultimate Orcadian seal of approval. "D'ye hear that young gerr-l at the cathedral?" I heard one Kirkwall shopper ask another in the local tea shop. "Excellent value for money."

No one, alas, could say that of the Giovanna d'Arco running as part of Covent Garden's Verdi Festival. An also-ran in the composer's catalogue, the opera has its moments but not enough of them. Much of the writing is feeble and the dramatic narrative - a romantic rewrite of history in which the lady's not for burning after all - inept. Only an inspired production with unimpeachable singing could save it, and the Garden comes up with neither. Philip Prowse's production is a shabbily vacuous spectacle that purports to explore the French connection between death, religion and La Gloire but is actually the sort of thing in which people endlessly march back and forth with banners because the director can't think of anything else for them to do. As for the singing, Dennis O'Neill is fine and Vladimir Chernov steals the show with some well-turned numbers, but the supposed star, June Anderson, is white-voiced, raw, and faltering. Hardly the Sutherland surrogate she once seemed. Daniele Gatti conducts with Italian eloquence but not much energy.

Davies's Symphony No 6 can be heard at the Proms: Royal Albert Hall, SW7 (0171 589 8212), 6 Aug. 'Giovanna d'Arco': Royal Opera House, WC2 (0171 304 4000), continues Tues & Fri.