At the end of a recent performance of The Magic Flute in Copenhagen, the curtain calls were interrupted by the Royal Danish Theatre’s chief executive Kasper Holten, who strode on stage to congratulate one singer in particular. Palle Knudsen, who had just sung Papageno, stood in his canary yellow costume as Holten handed him a wreath to mark his 25 years as a member of the company’s ensemble of soloists. Knudsen would soon be withdrawing from the stage, we learned, to take a management position looking after that very ensemble.

Knudsen is a model ensemble singer: versatile, charismatic and apparently ageless. Audiences in Denmark will have seen him sing everything from the title role in Sweeney Todd to Kovalyov in The Nose, and that’s just in recent seasons. Fixed in my mind is an unusually revealing portrayal of Count Almaviva. Just three nights after his anniversary and on the same stage, an ensemble singer at the other end of her career, Sofie Elkjær Jensen, starred in a new production of Eugene Onegin cast almost entirely from house singers. She and her colleagues did not disappoint, as I reported for this magazine.

And yet, the very idea of an operatic ensemble – a group of salaried soloists who form the backbone of a season’s casting – is problematic in an increasingly international age. The Royal Danish Opera’s ensemble recently said goodbye to Johan Reuter, a singer in his prime who could no longer reconcile its demands with his desire to sing specific roles and enjoy an international freelance career.

Reuter is not the first singer to have quit, finding the system ultimately constricting (though also served an admirable quarter-century). It works both ways. Often the ensemble system struggles to deliver on specialisms like coloratura or heroic/dramatic voices, resulting either in a frustrating compromise or the need to hire expensive guests. Locally, the comparison between the Royal Danish Opera and the Danish National Opera is stark: the latter company can wipe the slate clean for every production, hiring the specific singers it needs for each and every role, looking to up-and-coming voices from around Europe. There are no salaried soloists sitting on their hands for months on end because there isn’t a role for them to sing.

Those who defend the ensemble system do so vigorously and understandably. An ensemble of singers that works together year-in-year-out develops a sort of vocal telepathy and physical rapport, much like that of the great ensemble theatre companies. Audiences get to know them and feel more invested as a result, particularly when individuals step up to sing a title role. The culture of big name singers flying in for a single production – or for a handful of shows at the end of a particular run, as at Covent Garden – feels like a world away.

Or does it? With external financial support, the Royal Danish Opera is increasingly hiring guest singers for those demanding specialist roles its ensemble can’t adequately cover. It has needed to, in the Italian repertory in particular. The ensemble is strong (if not as strong as it once was) but there’s nobody obviously able to sing a world-class Violetta, Tosca, Aida, Radamès, Donna Anna, Tito, Siegmund, Wotan or Isolde.

Elsewhere in the Nordic region, the ensemble system has faltered altogether. It has been abandoned entirely at the Finnish National Opera, where there was once a corps of 25 permanently contracted soloists and now there are none. During her time at the Norwegian National Opera, Annilese Miskimmon – formerly of the Danish National Opera and now of English National Opera – tried to engineer more flexibility into a notoriously stringent ensemble system that bound singers into permanent contracts until they reached the age of 52. Miskimmon assured me at the time that she ‘believed in the ensemble system’, but her grapple with it proved frustrating for all concerned.

You’d think, in an age of vocal flexibility – when the ‘fach’ is dead, when singers increasingly surprise with their ability to stride over stylistic boundaries – that the ensemble system might be enjoying a heyday. But globalisation, high technical expectations and the desire to reduce fixed costs are apparently deciding otherwise. Many in the UK, meanwhile, bemoan the dissolution of the ensemble system here as they see British singers travel abroad, particularly to Germany where it still thrives, to benefit from its other great advantage: the chance to learn the profession by doing it full time, in one place, with a comprehensive supporting infrastructure.

At this point you might legitimately expect me to show my cards – to come down in favour of the ensemble system or against it. Sorry to disappoint. Week-in-week-out, I see examples of the system working brilliantly and failing miserably.

I’ll say one thing: I’ve often wondered what the cost benefit really is to keeping 20 solo singers on a salary, in relation to hiring bespoke solo singers from anywhere in the world for three months at a time. Then again, what would happen to the domestic singing ecosystem in a small country like Denmark if there weren’t ensemble contracts available?

It may be that the ensemble system is, curiously, better suited to a smaller, more local company like the Danish National Opera than an international-level one like the Royal Danish Opera. That would require it to be smaller, nimbler and more short-term. Is that a bad thing? Discuss.