It could be argued that the success of contemporary music at the Presteigne Festival is due to its promotion of composers who draw on traditional forms and tonal harmony. Perhaps, but the world of contemporary music has moved on from what some nostalgically describe as the heroic avant-garde of the 1960s and 70s. And contemporary music at Presteigne still demands concentration and an open mind, where concerts of unfamiliar music follow one another with a rapidity that scarcely allows the opportunity to draw breath, let alone eat in between. Sine Nomine International Touring Choir’s concert on Bank Holiday Monday morning, in the spacious parish church of St Mary’s, Pembridge, was a case in point. Over 90 minutes of recent a cappella pieces, by Gabriel Jackson, Cecilia McDowall and Paweł Łukaszewski, were relieved only by the better-known Choral Dances from Britten’s Gloriana.

It was an impressive effort on the part of Sine Nomine International Touring Choir under its conductor Susan Hollingworth, especially in the attractive but rather unforgiving acoustic of St Mary’s. Made up of choristers from across the UK, the concert was a superb showcase for the group’s discipline and refreshingly simple unfussy choral sound. Their pedigree was apparent in Britten’s Choral Dances, and they skilfully negotiated the striking harmonic idiom of Paweł Łukaszewski’s Two Lenten Motets. But the morning belonged to Gabriel Jackson, whose music is being featured as part of this year’s festival.

Composers are once again writing for choral forces in a way that many from a couple of generations ago shied away from, unable to reconcile the use of simple tonal building blocks for effective choral textures with the harmonic experimentation of the time. Gabriel Jackson has quietly established himself as the most serious and accomplished of Britain’s choral composers. Without resorting to the easygoing sound of the Whitacre, Lauridsen or Jenkins school, his music has intellectual seriousness of purpose and integrity together with an innate understanding of the idiom itself.

The concert’s opening item, Jackson’s O sacrum Convivium, now over 20 years old, has almost established itself as a contemporary classic, but the focus of the concert was his Requiem of 2008, lasting well over 30 minutes. Attempting, in the composer’s words, “to combine the solemn, hieratic grandeur of the great Iberian Requiems with something more personal”, it puts movements from the standard mass for the dead next to poems from other cultures and spiritual traditions. Built using the simplest of materials, its writing is often highly complex, splitting into up to ten parts, both feeling of the present time, yet also essentially timeless. Its quality of invention and ambitiousness place it as one of the most important contemporary works in this year’s festival and, to paraphrase Beethoven, one that surely will still be around in 50 years’ time.