It was a grim coincidence that in a week in which the Royal Opera staggered to the brink of the abyss and (maybe) back again it staged a piece whose text begins "What shall I do?" and whose originating plot describes a journey through the Slough of Despond and the Valley of Humiliation, with an assault of Doleful Creatures on the way. The piece was the Vaughan Williams adaptation of John Bunyan's The Pilgrim's Progress which played at the Barbican on Monday night. And if the Royal Opera's board members were following attentively, as opposed to sitting in the back row doing hasty sums with pocket calculators, they must have been consoled to watch how, after all his trials and tribulations, Pilgrim does actually make it to the Celestial City. As the text says: "He that is down need fear no fall/He that is low no pride."

They'd also have been pleased to see that the performance - a one-off, but to be repeated in Birmingham on 30 November - was a triumph: a magnificent finale to the series of Vaughan Williams operas which has been playing at the Barbican under the baton of Richard Hickox and the title "Visions of Albion". It has been a visionary experience in every sense; because even in these days of revived interest in Vaughan Williams's work, his operas have remained a no-go area. To ignore them is to ignore a major part of his output, in that the scores (six complete, one half-finished) span his entire mature creative life, from 1910 to 1958. But they have never drawn much critical acclaim or made it into even the interstices of the performing repertoire. And since they mostly predate that legendary night in 1945 when Peter Grimes opened at Sadler's Wells and proclaimed the viability of British opera, it's not surprising. Until that time, opera was assumed to be an alien medium for composers here; and with few opportunities to get British work into production, the prophecy fulfilled itself. Vaughan Williams's operas mostly came into the world via makeshift student stagings. The chance for him to develop something like conventional theatrecraft just wasn't there.

But in retrospect it has become clear that he did develop an unconventional feel for theatre. And whatever the limitations of The Poisoned Kiss, Hugh the Drover or Sir John in Love, there are qualities in Pilgrim's Progress which should be obvious to an audience comfortable with Janacek, Debussy, Philip Glass or any of the other 20th-century composers whose operas defy the standard dictates of well-made drama.

VW himself was coy about the operatic credentials of the Pilgrim. He called it a "Morality", and it plays like a pre-war village pageant (the sort of thing you find in Virginia Woolf's Between the Acts), with a cast of many small roles (though they lend themselves to doubling), epic choral hymns, and grandly static tableaux vivants. Deeply English, resolutely maverick, mystical and (as the man said) moral, it belongs to the tradition of benign, pastoral patriotism whose coordinates were framed by William Blake and Samuel Palmer. And it treats its subject with a robust, unsentimental sturdiness that opens out into a truly transcendental beauty. I have always loved it; always found in it the key to the entire, mature Vaughan Williams output - which it surely is, in that his personal progress toward completion of the score took nearly half a century, and passed through periods when the Pilgrim music was quarried for other pieces. Notably the 5th Symphony.

But does it really work? The premiere, at Covent Garden in 1951, was by all accounts a disaster. But an impressive student staging I saw at the Royal Northern College in 1992 suggested that it wasn't beyond rescue; and Richard Hickox's concert performance at this year's St Endellion Festival cleared up any doubts about the score. I described it in this paper as the most sublime musical experience I'd had all year. And so it was.

But at the Barbican, with the Royal Opera Orchestra and Chorus, a superlative cast, and simple but strong staging (semi-staging really), Hickox went one better and proved the power of the piece, not just in terms of spiritual lift but of enthralling theatre. Done democratically like a contemporary Mystery Play, with soloists emerging from the massed ranks of the chorus (who sat to the sides in front of the orchestra), it left only a cramped acting space at the middle-front of the concert-hall platform; and the decision to dress everyone in black polo-necks did initially make the whole thing look like a happening in a Christian coffee bar. All it needed was Cliff Richard to come on and save some souls over a cappuccino.

But it turned into an unexpectedly contemporary piece of work, a world removed from period pantomime and with a searing central performance from Gerald Finley, whose lean, agile but muscular-firm baritone caught exactly the balance between despair and determination that VW programmed into the role. One of the most confrontingly physical performances I've ever witnessed from an opera singer, it was also purely beautiful and touching, charged with energy and life. And with support from singers of the calibre of Susan Gritton, Gidon Saks, Rebecca Evans and the hugely promising Richard Coxon, it made a momentous evening. As for Hickox, it was the definitive achievement of his whole career to date: brilliantly done, with style and substance. If you missed it and can't get to Birmingham, the whole thing is going into the recording studio for issue by Chandos next year. If it doesn't sweep the Gramophone Awards I'll be surprised.

The Royal Opera, I should add, was lucky to get in on this particular act. The "Visions of Albion" series was essentially an LSO project, and it's not the sort of thing the Opera would ever have involved itself in but for the temporary embarrassment of its homeless state. Theologians might call it a Fortunate Fall, although fortune doesn't seem at the moment to be on the company's side in any other respect.

The Secretary of State's fired-from-the-hip proposal to merge the company with ENO would be worrying me if I thought it would ever happen. But it won't. ENO and the Royal Opera are two undeniably sick patients lying side by side in the hospital wing of the British arts, but you don't cure the sick by making them share a bed. Bed-sharing isn't treatment. It's economy. It's also the sort of sweeping socio-political gesture arts ministers make to raise the otherwise low profile of their jobs.

Richard Eyre's committee of inquiry must surely see that. And in the meantime the government seems to have been stung by the hostile reaction to its proposal. I had an interesting conversation on Thursday with Mr Smith's No 2, Mark Fisher, in which he took pains to tell me that the proposal was merely "a starting-point to break the deadlock and get the debate moving". In other words, a kite-flying exercise. As I understood the terms of what was first announced, it seemed considerably more than that. Why else would Chris Smith have declared a view at all if he intended to leave Eyre a genuinely free hand?

All other music matters have paled into comparative insignificance this week. The Wigmore Hall has been running a festival of Australiana but its supposed highlight, featuring the unlikely combination of Steven Isserlis and Barry Humphries, fell horribly flat with a programme of near-total trivia: nips and scrapes of cello introduced by random, tape-recorded ethnic ululation and a few jokes. The only thing that made any impression was a new and vibrant piece by Carl Vine for solo cello accompanying itself on multi-tracked, pre-processed tape (the methodology of Steve Reich's New York Counterpoint). Called Inner World, it was evocative, ecstatic, heartfelt: proof of the intelligent accessibility that places Vine, now, second only to Peter Sculthorpe in the natural ranking of Australian composers. Meanwhile, Jigsaw Music Theatre's new double-bill at the Bloomsbury Theatre proved very little beyond what one already knew: that this is an excellent little company with good singers, a valiant pit band, but unfathomable tastes in repertory. I Can't Stand Wagner (you can guess what it's about) and The Music Shop (a loose confection of Walton and Sondheim) are sort of fun but wafer-thin - written by two American composers, Seymour Barab and Richard Wargo, with nothing to say for themselves beyond technique. A waste of time for the performers, who include a good young character baritone, Giles Davies, and the exceptionally promising young tenor Henry Moss.

'The Pilgrim's Progress': Birmingham Symphony Hall (0121 212 3333), 30 Nov.