Allegri String Quartet, Wigmore Hall London

It is 50 years since the eminent violinist Eli Goren founded the Allegri String Quartet with second violinist James Barton, violist Patrick Ireland and cellist William Pleeth - rapidly establishing themselves as Britain's (and, indeed, Britten's) - best-loved quartet after the Amadeus. But where the older group cultivated a tremulous sweetness of sound, the Allegri always went for a plainer, perhaps more deeply penetrating manner - not to say, more adventurous programming. And this approach was maintained by Hugh Maguire when he succeeded Goren as leader, and passed on in turn to Peter Carter in 1976.

With the other founder-members long retired, Carter now finds himself veteran leader to a much younger line-up. Yet far from yielding to the loud "projective" brilliance of newer quartets, this 50th Anniversary Concert to a packed Wigmore Hall found the Allegri playing in a more intimate, genuinely chamber-music style than ever. Never more so than in their serenely unforced account of Haydn's wonderful String Quartet in B flat, Op 76, No 4 (the so-called "Sunrise"), with Carter feeling his way almost shyly into the radiant rising phrases of its opening and insinuating many a flexibility of beat and gliding of bow of a deeply traditionalist kind into its unfolding.

The Allegri approach also suited the fragile, sensitised textures of the opening movement of Britten's late String Quartet No 3, Op 94, and the reticent dignity of its passacaglia finale, even if they sounded a mite less focussed in the more brutal textures of the faster second and fourth movements. The central movement, essentially comprising an unearthly - and cruelly high - violin solo over the barest of accompaniments, was decently managed by Carter, though with a certain anxious pushing of tempo.

If this profoundly musical and vastly experienced artist has an Achilles heel, it is a certain instability of intonation under pressure - though, interestingly, exactly the same could be said of the leaders of at least two of our other finest quartets. At moments of the long, driving first movement of Schubert's String Quartet in D minor, D 810, "Death and the Maiden", Carter certainly sounded less than happy. Yet all went well in the texturally detailed, inexorably unfolding slow variations - with some exceptionally lovely playing in the second of them from the Allegri's current cellist, Paul Banda.

And where so many quartets play up to the quasi-orchestral weight and volume of Schubert's writing in the outer movements, the Allegri's refusal to grind out every sforzato at maximum force, far from constituting a weakness, enabled the work's complex ambivalence of mood and its many dark turnings of harmony to register all the more tellingly.