The Cloud of Unknowing is painted on a large canvas… Jeremy Filsell's flawless playing draws numberless nuances from Tonbridge School's Marcussen instrument. James Gilchrist is a passionate and occasionally volatile soloist… Jeremy Backhouse and the mighty Vasaris give this uneven piece everything they can muster. It is worth persevering with.

One sometimes writes, hyperbolically, of a performance moving one to tears. But at the end of Francis Pott's The Cloud of Unknowing, genuine tears were shed. In part that was due to the circumstances.This 80-minute oratorio for choir, tenor and organ was written in response to the wars and atrocities of the past five years, and specifically to the July 7 bombings in London. What's more, it was being given its premiere (in the London Festival of Contemporary Church Music) at St Pancras Church, close to where many were caught by the bus blast.And if memories of that day were not sharp enough in Londoners' minds, the unscripted wail of police sirens during the quiet final pages of Saturday's performance, subliminally reminded us that the cycle of hate and violence goes on and on. That, and a heartfelt plea for reconciliation and tolerance, is very much the theme of Pott's oratorio. But the work is far from being simplistic peace propaganda.The 48-year-old draws his texts from the psalms, war poets, Blake and other visionary writers, and a mystical medieval tract. Often the tenor (James Gilchrist, superb) takes the part of human conscience, crying in vain against the chorus's war-cries. But in the glorious epilogue it is the chorus that calls for a "blind stirring of love", in a stupendous outburst of rich polyphony - wave upon wave, gloriously sustained. Any choir would find the piece a challenge, not least to its stamina. But Jeremy Backhouse's excellent Vasari Singers performed it not just accurately, but with bags of heart and soul as well. The Cloud of Unknowing deserves a concert life beyond this moving performance.