James Bowman, St Martin-in-the-Fields, London

Where would "early music" have been without James Bowman? Probably not in the flourishing state it is now. And would the counter-tenor voice be the fashionable thing it is today, if he hadn't kick-started its emergence from the shadowy, over-refined realms inhabited by Alfred Deller? When Bowman breathed life into Britten's Oberon, and went on to incarnate Handel's heroes with burnished authority, the voice that had been banished to the liturgy was brought back centre-stage. The mountain of Baroque recordings he's created over the past 40 years all bear witness to his uniquely powerful and expressive sound.

Breezing into the spotlight, he looked like a genially substantial after-dinner speaker, and that is how he came across as he introduced his first aria from Messiah, "How beautiful are the feet", which is usually sung by a soprano. We listened with bated breath: Bowman is now 66, an age where the voice – especially an "artificial" one such as his, requiring a particular kind of muscular effort – has normally begun to decline. We needn't have worried. It took him a minute to get into gear, with some top notes sounding awkward and pinched, but all the artistry was there in the exquisitely shaped phrases, even if the crystalline clarity of his youth had gone.

Next came a rarity in the form of a setting of Purcell's "Music for a While", which Bowman gleefully warned us would sound a bit like Brahms, with its usual harpsichord/viola da gamba accompaniment replaced by the eight string-players of London Octave, whose superbly delivered Bach and Handel framed the evening. This was one of Bowman's signature tunes, and it was wonderful to find it still sublime in this new instrumental garb. Where Bowman's one-time pupil Andreas Scholl simply floats his notes, Bowman invests every syllable with urgent meaning; the spell he cast was extraordinary.

Two more arias from Handel saw him filling the big church with his clarion sound, and in winding up with the "Agnus Dei" from Bach's Mass in B minor, he showed what steely beauty lay behind his deceptively light approach. Having forgotten to bring an encore, he unapologetically sang the Purcell again, even better. It was nice, as he observed, to escape briefly from the coils of the authenticity police.