The celebrated organist, Dame Gillian Weir, is at the heart of a life-affirming festival of the works of Messiaen. Christopher Dingle met her
Gillian Weir is enthused. Anyone who has experienced the renowned organist perform, give master classes or seen her television appearances will hardly be surprised. Music palpably excites, consumes and inspires Weir as much now as when she first burst onto the scene in the Sixties. Josquin, Bach or Franck could have stirred her passions, but today the catalyst is the forthcoming festival at Westminster Cathedral, "The Celestial Banquet", celebrating the 90th anniversary of the birth of a composer with whom her name is often thought synonymous, Olivier Messiaen.

While for many Weir performing his complete organ works (including the first chance to hear a recently rediscovered short work, Monodie) is enticement enough, The Celestial Banquet is not content simply to be a series of recitals. Weir and James O'Donnell (master of music at Westminster Cathedral) have devised an event in which pre-concert talks, plainchant, poetry, Messiaen's writings and the scriptural prefaces to his works will combine with imaginative musical juxtapositions to build a fuller picture of Messiaen's spiritual world. Dufay's Missa L'homme arme, for instance, will intertwine with Messe de la Pentecote (Messiaen's expression of faith through the language of the "brave new world" of the 1950s), and movements from the piano cycle Regards sur L'Enfant-Jesus will be introduced into the popular Christmas work La Nativitie du Seigneur.

The venue itself is central to this exploration. "The organ at Westminster Cathedral has the overwhelming power that is crucial for Messiaen," effuses Weir, "it makes a simply fabulous sound and there is no better building anywhere. It has a tremendous acoustic and the ambience is wonderful." However, she stresses that the composer did not want a bathroom acoustic. "Many people play it in the kind of atmosphere where you cannot hear a single note. Messiaen wanted clarity in the way his ideas were presented and understood, and clarity in the music." One reason that many other interpreters fail to achieve this limpidity is their tendency to make what is complex, too complicated. "Messiaen wanted to escape spiritually and technically from the idea of limitations. He uses technical points to express ideas, but these ideas in the end are emotional."

Weir is patently sympathetic to the notion of music as emancipator of the soul, expressing frustration at those for whom it is merely an intellectual exercise. "I think we are terribly afraid of emotion at the moment. That is a tragedy. If you are going to write a piece of music, it has to be written from the need to say something." Nor should performers allow music to ossify, but rather ask themselves: "What have I got to say about this piece that has to be said, that is going to make somebody leap in the air?"

Like many musicians, especially organists, Weir is contemplating what she has "got to say" about Bach in 2000, the 250th anniversary of his death. In the short term, however, she confesses that she will need a holiday after the festival. This is said with the same degree of expectation as people who "need" to win the Lottery, and it is no surprise that she is in fact attending the National Convention of the American Guild of Organists where, along with performing Messiaen's Meditations, she is giving numerous lectures and master-classes.

Those hoping for technical tips will instead find themselves challenged to peek above the parapet of the score. "I find that, especially in America, people concentrate on the complex rhythms, practising them until they are as perfect as a computer could produce, but thereby suppressing the freedom for which Messiaen devised them." The mechanistic approach prevalent among many younger performers leaves Weir exasperated. "Students say 'how do I play this ornament?', not understanding that an ornament is the kind of thing a bird does when it gets up in the morning and says "Hey, it's spring!" It is spontaneous. Rules govern the general principles, but the spontaneity has to be there."

Nature was a profound source of inspiration to Messiaen and the songs of hundreds of birds appear in his music. These ornithological aspirations are well documented, but he also portrayed many other natural phenomena including rivers, mountains, trees and even crickets, prompting Weir to observe that he was "really a painter who happened to work in music".

Whilst unconvincingly professing an ignorance of painting, Weir's desire for greater efforts to be made to relate music to the other arts bubbles to the surface in the guise of her passion for poetry. "The abandon and extreme emotion found in John Donne and other metaphysical poets is reflected in composers like Messiaen and Alain - "Death, be not proud, though some have called thee Mighty... death, thou shalt die" - that for me captures precisely the mood of "Combat de la mort et de la vie" from Les corps glorieux, which is about death being overcome and metamorphosed into life."

"Combat de la mort et de la vie" helped to launch Weir's career when she won her first competition, the 1964 St Albans International Organ Festival. Before long, she met Messiaen, impressing him so much that, in 1972, he gave Weir the manuscript of Meditations sur le Mystere de la Sainte Trinite for her to perform the British premiere. Advocacy of this 20th century giant is a consistent feature of her activities and recent years have seen a substantial contribution to Faber's The Messiaen Companion, whilst her release in 1995 of the complete works on Collins Classics heralded a chorus of acclaim.

Despite many plaudits, including being made a Dame of the British Empire in the 1996 New Year's Honours list, Weir is not content to rest on her laurels - the inventive and provocative programme of The Celestial Banquet testifies to that. "The essence of Messiaen's music is joy. A joy that is not just a naive immersion in a warm bath of religiosity, but a driving energy that is the wellspring of creativity and creation." It is an ebullience which Weir shares in abundance.

'The Celestial Banquet' concerts will take place every Tuesday from 12 May until 16 June. (0171 798 9055)