London Philharmonic, Royal Festival Hall, London

In addition to her recent Contemporary Music Network tour, Kaija Saariaho has just a single work in each of three London Philharmonic Orchestra concerts between now and May. In the first of these, on Saturday, Graal Théâtre was surrounded by 20th-century classics from France and Finland.

This was appropriate, since the composer has lived in Paris for most of the last 20 years; Anthony Burton (who gave a valuable pre-concert talk in her absence for Paris performances of L'amour de loin) suggested that these days she is more French than Finnish. In recent interviews, Saariaho has been quite critical of Finnish musical life, though that doesn't stop her from continuing to benefit, like Magnus Lindberg, from the considerable state support Finland offers its creative artists.

Graal Théâtre (Grail Theatre) is a substantial violin concerto lasting almost half an hour. First heard at the 1995 Proms, it was written for Gidon Kremer, who played it here as fabulously as he always does. Alan Gilbert and the LPO rose well to the challenges of the kaleidoscopic part for large orchestra that surrounds the soloist.

Beginning and ending with a single triangle stroke and an extraordinary range sounds from the solo violin – glassy harmonics, tremolandi, glissandi, variations in bow pressure and much more besides – Graal Théâtre sweeps up such extended techniques, commonly associated with Modernist music having a very different agenda, into a pair of highly expressive, sonically alluring, incident-laden and persuasively goal-directed dramas. The first movement is intermittently obsessed (again, in a rather anti-Modernist kind of way), with small repeating patterns and, amid its massive, searing climaxes, throws up a riveting duet between the solo violin and first trumpet. The shorter second movement starts with a positively seething violin cadenza, the confrontational impact of which reverberates for more than half its length.

Graal Théâtre is a transitional work in Saariaho's output, demonstrating her recent concern with line, both melodic and narrative, without sacrificing the timbral focus of the music by which she first became known. It's also a complex work, scarcely yielding all its secrets, including those of its title, at once. Yet I'm convinced that, as crucial transitional pieces can often be, Graal Théâtre is a great composition, perhaps the best thing this composer has done.

There is insufficient space here to praise the conducting of Alan Gilbert, an American previously unknown to me, in the rest of this programme. An uncommonly secure technique was already much in evidence in Ravel's Le tombeau de Couperin. His account of Sibelius's Fifth Symphony, though similarly a bit clinical early on and, curiously, at the ending of both the first two movements, developed into a performance that combined unusual clarity of texture and phrasing with some real understanding of this music's symphonic undercurrent. We shall surely hear more of Gilbert here soon.