I was asked, more than once, after last night’s concert in the City of London Festival, by Jan Garbarek and the Hilliard Ensemble if I’d noticed a magical glint of sunlight falling across the nave of St Paul’s Cathedral. That’s what this music does to people. A contemplative, 90-minute set from these unlikely co-conspirators, who have worked together now for nearly two decades, brings people to a particular sense of calm, wonder, and midsummer magic. Definitely no jostling, then, as the crowd which had filled every seat in St Paul’s Cathedral made its way peacably and good-humouredly back down the nave and towards the west door. Who knows quite why or how it works, but we’d all got a definite lift from it.

The Garbarek/Hilliard phenomenon affects large numbers of people. Sales of the first CD Officium, released on ECM in 1994, are now well into the hundreds of thousands. Some of last night’s audience- at this third concert by the Hilliards and Garbarek in St Paul’s cathedral – were clearly late converts: there were yet more copies of Officium being sold after the concert last night. So -evidently- the reach of this music still grows. The second album Mnemosyne is ten years old. And…. ever so quietly….. rumours are reaching me of a third, ere long. Ssshhh.

But there are important differences between the live and the recording. Firstly, the setting of St Paul’s which occupies your eyes is quite majestic. Those vast gold vaultings give a Byzantine feel. And the echo, at least five seconds of it, colours every sound which Garbarek and the Hilliards -all performing without amplification – make. This kind of building just takes the sound off the musician, and sends it swirling round and round and back again. The group were also wandering into different recesses of the building, sending music out from unexpected places, using the space extremely cleverly. Gordon Jones, on one walkabout, switched to throat-singing. That was particularly effective

There was no set-list available, but the group do a combination of works from the records, plus they keep adding new repertoire. The Hilliards switch effortlessly from medieval to modern. The final numbers. a “Remember Me” and an “Agnus Dei” were solidly, understatedly joyous. Garbarek improvises freely, sometimes sets up call-and response with the quartet. Sometimes he’s on pitch, at other times he used the natural vagaries of saxophone tuning and overtones, particularly on his vintage curved soprano sax to create less cultured, more earthy shrieks and yowls.

There was also a moment which seemed to bring a mischievous smile to Garbarek, on solo tenor saxophone. He sent out first a series of rising minor thirds, getting cumulatively louder, and then a row of sonorous, low honking B flats, chasing each other around the cathedral. How satisfying as a saxophonist, how impossible to resist, to hit home hard , low and powerfully into every last corner of Christopher Wren’s vast echoing masterpiece.