THEY HAVE have probably performed more carols over their 35-year history than there are Christmas lights twinkling on Oxford Street. Yet with inexhaustible energy the King’s Singers are off on another Christmas tour of the United States, leaving audiences at home with a new album simply entitled Christmas. Listen to it, or catch the King’s Singers in a Radio 3 Christmas Day broadcast of their recent concert at Grosvenor Chapel in Mayfair, and you will hear that they sound as fresh as ever.

This is a very different programme from their last Christmas album of a decade ago, which featured souped-up carols with an orchestra under Richard Hickox and no less a soprano than Kiri Te Kanawa. The new programme returns to their traditional sacred roots with some of the least tacky Christmas music you will encounter all season. Its sober tone will surprise those who think of the King’s Singers as sort of musical Pythons.

One of the group’s special achievements has been to maintain their act without going stale. True, some serious music lovers might sniff at the idea of a King’s Singers concert, but anyone who has actually heard the group recently will find their style hard to resist. It’s natural to assume that a group such as this might have lost their original identity, yet the uniquely smooth blend of just six male voices — in the slightly unusual configuration of two counter-tenors, one tenor, two baritones and bass — remains undiminished.

Some other British musical institutions of similar vintage must be looking on enviously. The Swinging Sixties were good years for classical music in London, with the emergence of groups who were to change the way the world thought about performance style. But that same change eventually saw many of them being left behind or superseded — while no one has yet managed to beat the King’s Singers at their own game.

Two orchestras that once played a vital role in moulding taste come to mind. The Academy of St Martin-in-the-Fields and the English Chamber Orchestra challenged the way Mozart and his predecessors were being played, but although they continue valiantly, the booming business of period orchestras has pulled the musical rug from under their feet. Yet while there has also been a burgeoning of small vocal ensembles, none of these choirs can quite match the King’s Singers in their mix of sheer musicality and ability to entertain.

One key to the group’s success has been their stability. Over the years, their hairstyles have altered more than their personnel, and the King’s Singers can boast of having had just 18 members over their long existence. All that has changed is the connection with King’s College, Cambridge. Though it happens now that one singer is a former Kingsman, the link was loosened when the first departure of a member — ten years to the day after the group’s founding — brought the realisation that they could not continue indefinitely as a group of college friends. Though they remain rather respectable fellows who just happen to be as good at singing silly songs as serious ones, the only background they tend to have in common now is the solid training they all received as cathedral choristers.

Often described as “the finest vocal ensemble in the world”, they are still in demand everywhere, from the Hollywood Bowl to Windsor Castle. Not long ago their concert in a Korean football stadium featured a live TV broadcast and police escort — not to mention the cult status bestowed when the audience’s cigarette lighters came out. To borrow the title of the Malian group Orchestra Baobab’s recent hit album, they are “Specialists in All Styles”: famous for putting the fun back into early music, they sing everything from sacred a capella music via folk and modern works to pop encores.

Everything comes with their trademark, slightly camp humour. After all, in those countries where they are biggest — the USA, Germany, Italy, the Netherlands — they have to appear as British as possible. Only about ten of their approximately 100 concerts a year take place at home, but then perhaps it is only Britain that has tired of British humour. In America they play the quaint card, and in Germany they seem to share their fans with Monty Python — though there is a big market there for their serious church concerts, as well.

The group’s very polished, and maybe sometimes a little too knowing, presentation style includes one very un-British feature: talking to the audience. Not just the on-stage humour — something that they have developed organically, for off-duty these chaps would not claim to be funny at all — but the post-concert chats with audiences.

They never give a concert without greeting their fans in the foyer, and this kind of cultivation has certainly paid off. The King’s Singers are almost as much of a commercial phenomenon as a musical one; they reportedly are able to earn fees undreamt of by most choristers.

They have also created a distinguished body of work, having commissioned more than 100 new pieces. The roll-call of composers who have written for the King’s Singers is impressive, and includes Berio, Ligeti, Penderecki, Rorem and Maxwell Davies. Even on their new disc the old traditions of Christmas are not allowed to stifle the new: living composers are well represented, with highlights including the liveliest number by the old “holy minimalist ” Arvo Pärt that you are ever likely to hear.

• The King’s Singers are on BBC Radio 3 on Christmas Day at 6.15pm. Their new album, Christmas, is on Signum Records SIGCD502