With sixteen boys and fourteen men, it’s arguably the world’s most famous choir whose annual Christmas broadcast plays to millions in the farthest corners of the globe (mud huts in jungle clearings not excluded).

It’s been functioning since 1441. And tomorrow the illustrious King’s Cambridge Choir will be in Hampstead Garden Suburb for this year’s St Jude’s Proms - with a choirmaster who wasn’t there in 1441 although it sometimes feels like it because he’s been in charge for 35 years. Stephen Cleobury. 35 years is a long time, and it begs two frequent questions: starting with the way the choir has changed over the years. When Cleobury took command in 1982 he followed Philip Ledger. But still very much around then was Sir David Wilcocks who had nurtured through the 1960s-70s the famous King’s sound: soft, luxurious, slightly precious, very English, heavily dependent on the floating resonance of the College Chapel and contrasting with the harder ‘Continental’ tone of the rival choir at St John’s, Cambridge.

But, as Cleobury says, “over time, that polarity has reduced, and the two choirs have moved towards each other, meeting somewhere in the middle. To what extent I’m responsible I can’t say: I haven’t consciously set out to change the sound, but I’ve changed the repertoire which no doubt has an effect. It’s a wider repertoire now than thirty years ago, and with more modern music.

“I began the regular commission of a new carol for every Christmas Eve, and I’ve made a point of approaching composers outside the world of Anglican church music: people like Harrison Birtwistle, who was so enthusiastic he wrote us a piece that ran for six minutes. The shortest has been Arvo Part whose carol came in at barely one”.

Another factor for change has been the constant turnover of voices you get in a student choir where a third of the back row are new every year.

“There are pros and cons to that”, says Cleobury. “Yes, people come and go. But they’re always young voices, which are easier to mould into a good blend. And they’re always fresh: they don’t have long enough doing the job to get fed up with it.

“Being students with lives to live other than being in the Choir, there are sometimes issues about the commitment required to function at the highest standard of vocal discipline. But they know what they’re taking on when they apply, and there are very few real problems”.

There are also fewer problems these days with the Senior Common Room. 35 years ago, King’s SCR was seriously secular and hostile to the Chapel. These days the relationship is easier – helped, you might assume, by the financial contributions that the Choir’s commercial work brings in. But Cleobury says that’s not the case.

“The Choir isn’t a money-maker: all the tours, broadcasts and recordings earn less than you’d think. And set against what it costs to provide bursaries for boys in the choir-school, we’re certainly not accumulating profits. But the College does recognise our importance in attracting donations. And there’s broader acknowledgement now that we’re engaged in the same pursuit of excellence as the other academic disciplines in the SCR – which fosters respect beyond the Chapel-goers. There’s no threat to our existence any more”.

The only question - and the second of the two that Cleobury constantly gets asked these days - is how much longer his own personal existence with the Choir will carry on. But there’s an answer now: he’s planning to retire “in two to three years ” - which means choirmasters throughout the western world are dusting down their CVs, ready to succeed him. That may not be an entirely comfortable experience for Stephen Cleobury, but it’s ego-massaging to know you have the job that everybody wants.