Harry Christophers is conducting proceedings with an air of good-humoured, calm efficiency. “Sops, don’t overdo it on page three, second bar. Tenors, much, much more words, really expansive. Let’s hear your alleluias.”

This is a rehearsal of top-level professional choir The Sixteen. Christophers is conducting with one hand and holding a harmonica in the other — for use in checking that the singers are in pitch.

The Sixteen is rehearsing for its 2009 Choral Pilgrimage, which will see the choir give 27 concerts across the UK –— including the University Church, Oxford, on Saturday, March 14. Oxford is particularly appropriate, because the group was founded by Christophers just up the road at Magdalen College, and this year it celebrates its 30th birthday. The Sixteen’s administration used to be run from Oxfordshire, and CORO, The Sixteen’s own record label, is still based in the city centre.

“I was an academical clerk in Magdalen’s choir,” Christophers explained during a rehearsal break. “There was a gentleman called Peter Nelson who regularly came to evensong, and he particularly loved Tudor music. When I and two or three others left, he felt it was the end of an era for him. So he quite simply asked me to put on a concert of his favourite music. And that’s how it started. The name of The Sixteen came a year or so later.

“It was all very new to me. I’d done quite a lot of conducting in various ways at Oxford, and I sort of knew what I wanted to do, even back then. But the interesting thing was that the group was full of people of all ages — I think that’s been our trademark ever since. Two of my original group are still official, regular members of The Sixteen, but — nice for me — another four are now directors of the company, overseeing the well-being of the choir.”

Besides The Sixteen, Christophers regularly guest conducts all over the world, and has recently been appointed artistic director of the Handel and Haydn Society in Boston.

Besides celebrating The Sixteen’s own 30th birthday, the choir’s Oxford concert will mark two other anniversaries — Purcell was born 350 years ago this year, and James MacMillan will reach 50.

It’s an odd pairing at first sight, but you’ve only got to listen to a rehearsal for a few minutes to discover how well the two composers do, in fact, complement each other. When, I asked Christophers, did The Sixteen start to extend its range into contemporary music?

“For many years the accent was on the 16th century, and trying to give our own stamp to it — mainly trying to make sure that 16th-century English music didn’t sound like 16th-century Spanish, or Italian, or whatever.

“I soon wanted to add Baroque music — it’s rather nice coming from the 16th century to the Baroque, because you’re evolving the style out of the Renaissance period. The later forays into the 20th century are very important for the choir — it gives them something else to do, and it’s amazing how the sound of Renaissance music suits the sound composers want in the 20th and 21st centuries.

“Also, when you’ve got your own group, you can reflect the music you love. Maybe we’ll do a Strauss motet one day, for instance. I’d love that.

“But, once, we went to Moscow, to Valery Gergiev’s spring festival. He wanted us to perform Russian music, Rachmaninov. I said, ‘no way, this is coals to Newcastle’. And they said, ‘no, we really want to hear what it sounds like’. They wanted to hear the chords, and a different interpretation. We were very nervous about it, and it was hard because we were in an acoustically dry theatre — you’re not allowed to perform concerts in the churches there.”

The Sixteen has so far recorded some 90 CDs, several of which have picked up prestigious awards.

But, for him, Christophers revealed: “There is nothing like a live performance; the feeling of singing out to an audience. As the years go on, I try to put more rough edges on the CDs, just to make them sound human.”

lThe Sixteen perform Purcell and James MacMillan at the Uinversity Church, Oxford, on Saturday, March 14. The concert will be preceded by a conductor-singer encounter. Further details at thesixteen.com and tickets on 01904 651485 or online at ncem.co.uk