LSO / Gardiner, Barbican, London

In a masterpiece of understatement, posters outside the hall spoke of a "small change" to the programme. Since it involved replacing one of Beethoven's shorter overtures with the entire Fourth Symphony, you wondered what qualifies for a big change: adding the complete works of Mahler, perhaps. Yet the concert mysteriously did not get any longer, and finished around the time you would have expected had the London Symphony Orchestra's principal, Sir Colin Davis, been conducting the programme in its original short form.

Maybe not so mysterious given that the conductor was Sir John Eliot Gardiner. At the end he dispatched the mighty Fifth Symphony, with all its repeats, in 28 minutes. Now that was a bigger change than anything at the start of the show. Taking 20 per cent off the usual duration, while playing more music, seems like a caricature of what graduates from the early music movement do to familiar pieces. Far from diminishing the symphony's power, however, the performance intensified and heightened it.

The LSO can get round the notes physically faster than Gardiner's period-instrument orchestras, but so relentless was the drive and so firm the rhythmic impetus, that this went way beyond a "look what we can do" experience. Substantial elements of period technique, coupled with a reduction of the string sections, kept the balance clear and avoided any sense of scramble.

There were some irritating squeaks on the horns, as players of modern valve instruments pretended they had old ones, but mostly this spring-clean was nothing but positive. Initially the blast of sound at the arrival of the finale seemed an anticlimax, so speedily was it sent on its way, but soon the onward rush and the assertive brass developed a vivid, rather French character that renewed the music's shocking sense of liberation: once associated with the European events of 1789, it was immediate enough to put a modern audience in mind of 1989.

What worked well on the Fifth had put on a less happy show in the Fourth. Sure, it is good to be reminded that this too is a concentrated piece, but the character is more genial and pace can be counterproductive. Not for nothing did Beethoven write "ma non troppo", not too fast, over the finale. Played "troppissimo", as here, it loses its good humour and becomes impatient. Much the same went for the other quick movements, in which attempts to lighten the phrasing sounded like a mannerism, and the best things in the symphony were its hushed explorations and its expansive slow movement.

The First Piano Concerto, with Piotr Anderszewski, was a meeting of unlike minds. For much of the time Gardiner had to take a more spacious approach, and the music had time to breathe. Anderszewski was dynamic, and his breadth and warmth of phrasing extended to the orchestra in contrast to its self-conscious shaping of the previous work. Striving as ever beyond the possible, he pressed down so intensely on one sustained note that you half expected the keyboard to produce vibrato. Anderszewski's pounding left-hand accents gave a folk-dance touch to the centre of a headlong finale.