BBC Symphony Orchestra, Sir Andrew Davis, Barbican

Elgar and Delius are two geniuses who only ever composed themselves - the first drawing heavily on psychology and physiognomy, the second drenching his country visions in painful nostalgia. So it made good sense to have man and nature side by side in Sir Andrew Davis's latest enterprising concert. Oh, and there was a commission from the Royal Philharmonic Society's Elgar Bursary too, though this was only "new" music by the old guard.

Why so harsh? Because first you need ideas, and then you need the right means to clothe them in, and the orchestra's your toy given such a title. Not a single line, idea, theme, call it what you will, in Roxburgh's new work struck me as fresh or original, and his instrumentation, mostly thickly applied, seemed far less suggestive of the proposed "concerto for orchestra" than any Strauss tone poem, Mahler symphony or John Adams orchestral work, if we're talking about showing off groups or individuals within the larger ensemble. Very well, so maybe the 74-year-old composer's vague definition - "The work requires a very soloistic characterisation from every player in the orchestra" - might apply to the difficulty of the piece, and all credit to Sir Andrew and his players for keeping outlines and rhythms sharp and clear. But when there's not much to say, it seems like so much wasted effort.

In brief interludes of a more truly soloistic character, Richard Simpson's sterling oboe work and Daniel Pailthorpe's delicate flute made their mark. But the percussion was used in that unimaginative, washy way so endemic among many new scores, reminding me of those grim days in the 1980s when one endured so much by the British music establishment that left no mark (and I can't remember a single thing about the Roxburgh works I would have heard in Edinburgh during that time). I like to think we've entered a more communicative age. But Roxburgh, who said nothing to me at all in this piece, isn't part of it.

Enter - hurrah! - Sir John Falstaff to make us laugh and cry, in this instance a disconsolate portrait of that most faithful Shakespearean-in-music Sir Edward Elgar, his failings and his hopes. The dark, selective colours struck us at once; the musical ideas teemed, so much so in Davis's passionate nuancing that I imagine even anyone who didn't know the episodes from Henry IV Parts One and Two pictured within would still have relished the cornucopia of invention.

Whether in the brassy swagger of Hal, the man born to be king, or the slightly troubled dreams of Jack, once page to the Duke of Norfolk, Davis's identification with the vividness of the score seemed total. He was rewarded with nimble dancing cellos, superb solo string-work from Stephen Bryant and Graham Bradshaw, and the hiccoughing, grandiloquent Eastcheap bassoon solo of Graham Sheen. The deathbed scene, our old friend babbling of green fields in the tenderest vein imaginable, was supremely moving; but I was in tears long before that.

As indeed I'd hoped to be, and been told I would be, but wasn't, quite, in the vast work for orchestra and chorus many believe to be Frederick Delius's masterpiece, The Song of the High Hills, completed around the same time as Elgar's "symphonic study" in 1912. People will tell you that Delius drifts, especially when he's musing on the mountains of his beloved Norway, but there is strength of purpose behind this progression from sighing cares to a vision of "the wide far distance - the great solitude", as Delius writes in his score.

We have to go through all that hand-wringing to reach the plateau in question, as a cushion of strings leads in distant choral voices. The heart of the piece is all celestial twitterings and awed contemplation, woodwind solos of Grieg-like freshness leading to a big choral climax as the natural vision fades and man is left to his own devices, with only the embers of the epiphany glowing right at the end. All that was missing was a theremin or an ondes martenot to swoop deliriously around the choral ooh-ing and aah-ing.

It all sounded rich and gorgeous, with Davis giving enough forward impetus in climaxes to keep any hint of torpor at bay, but the sound is perhaps more important than the substance, and no doubt this is one work which the notoriously unco-operative Albert Hall would have given a much-needed halo. Still, Delius is desperately out of fashion, and I guess I was grateful for the chance to hear this large-scale piece of nature-mysticism made flesh.

• The BBC Symphony Orchestra celebrates its 80th birthday in a Barbican concert on 22 October
• Find Sir Andrew Davis's Elgar recordings on Amazon
• Listen to this concert for the next week on the BBC iPlayer
• See what's on at the Barbican this season