Five thousand miles away in Utah, the King’s Singers are getting excited about two very special concerts they’ll be performing at the Royal Albert Hall in London on 6 December.

“It doesn't get much better than the Albert Hall,” Jonathan Howard, bass, tells me.

Fellow vocalist Timothy Wayne-Wright, countertenor, agrees: “Not only that, singing with the RPO and with our old friend John Rutter, who has such an amazing gift – it’s going to be a really special night.”

Indeed it is, one brimming with sing-along carols, rousing fanfares, festive works and John Rutter's annual quiz, all guaranteed to fill the audience with Christmas sparkle and Yuletide cheer.

When we speak, Tim and Jonathan, plus the remaining four members of the legendary vocal sextet, are coming to the end of a three-week tour spanning the US from east to west. They flew into New York and will leave from Los Angeles. They won't be gone long, though. They’ll be back next year – in fact, three times.

“It’s why we have so many air miles,” says Tim, laughing.

I’m talking to the two singers over Skype. In view of their globe-trotting lifestyle (the group is big, not only in the States but Australia, the Far East and, closer to home, Europe) it’s a medium they’re clearly comfortable with.

“It’s perfect for keeping in touch with friends and family,” says Jonathan. “We’re touring and performing for 200 days each year. You need that face-to-face connection.” 

Next year will mark the King’s Singers’ 50th anniversary (the group was formed on 1 May 1968). It’s a remarkable achievement given that when the group was formed by a group of recently graduated choral scholars from King’s College, Cambridge, its style of a cappella (or unaccompanied) performance wasn’t in vogue.

“It wasn’t cool,” says Tim. “But then the group has always done things others weren’t prepared to.”

‘Uncool’ things like actually engaging with their audience and looking like they were enjoying themselves, performing repertoire from across the musical spectrum and occasionally breaking into ‘vocalisations’ – all things never before seen or heard in a classical concert hall.

Still, while traditional concertgoers might have been uncomfortable, the wider public soaked it up. The King’s Singers became a popular fixture on television throughout the 1960s and ’70s, both in the UK and the US. Fast forward to today and the group’s style of singing has never been more in demand.

“A cappella is thriving across the world,” says Jonathan. “It’s been helped by the popularity of shows such as Glee and The Sing-Off. We’re fortunate to be the beneficiaries.”

That may be so but what both members are keen to point out is that they’re success has never – and will never – be at the expense of musical quality.

“It’s a huge responsibility bearing the weight of those six founding voices,” says Tim. “We’re not crossover. To be so, would diminish our music merely to make it popular. The King’s Singers has survived by not being led by fashion, only by what sounds good for the voice.”

Jonathan continues: “Of course, when we create programmes we’re concerned there should be something for everyone. We’re not biased against genres be they of the church, the concert platform, the theatre or the pop world. We happily perform them side by side to the best of our ability. Ultimately, we’re concerned that whatever we do allows the music and our voices to shine.”

Despite the fact I’m seeing Tim and Jonathan over a fuzzy Skype connection, it’s obvious from their ages they weren’t doing their vocal exercises in 1968… So what was that KS sound first minted all those years ago, and how is it preserved and passed down the line?

“The sound was and remains breathy and perfectly blended,” says Jonathan. “It’s six voices sounding like one. Saying that, we work hard to find voices that complement each other.”

Finding those voices, the torchbearers for the next generation of audiences, is the key.

“No one applies for this job – you’re recommended,” says Tim. “In the audition people sing with us and not to us. They rehearse with us and that way we – and they – get to hear how they fit vocally and personally.

“I liken it to when you first move in with your girlfriend – you never know until you work with a new singer if it’s going to work. Fortunately, we haven't got it wrong, yet!”

A confident claim indeed but one with which those lucky enough to be present at John Rutter’s Christmas Celebration at the Royal Albert Hall on 6 December are sure to agree.