"Organising 70-plus people in a room is no holiday. It's a feat of concentration - especially when you've only got seven weeks. That's about the same rehearsal time we give a Cheek by Jowl show: but Cheek by Jowl is just a handful of actors. There's so much more here. Just getting everyone through the door takes forever."
More conceptually, the problem is the given premises of opera. "In a play the director 'conducts' the piece. Shakespeare is more limited - the iambic pentameter sets up rules about pace - but effectively you cue everybody in. With opera the timing is out of your control. The emotions, too, are largely supplied: you have to take them from the music. And it's banal, I think, when a director tries to upstage what's in the score."
For audiences used to directorial opera-theatre, where staging and music are in constant conflict, these will be sweet words. But Donnellan isn't all passivity. He draws a distinction between going against the music and going against its rhythm - "which is sometimes interesting: for example, if the score is frantic and you put a kind of stillness on the stage. I think that can be legitimate". He also distinguishes between challenging the text (beneath the belt) and challenging perceptions of the text (invigorating).
Perceptions of Mahagonny generally place it in the realms of Marxist didacticism. A product of the collaboration between Bertold Brecht and Kurt Weill that also generated The Threepenny Opera and The Seven Deadly Sins, it is effectively an operatic take on the abrasive cabaret-theatre of 1920s Berlin. Heavy with sardonic bleakness and epic moral tone, it tells the story of a city - Mahagonny - dedicated to pleasure and the gratification of desire, its only rule: Do as you will, so long as you can pay for it. As indictments of capitalism go, the message isn't veiled.
But Donnellan doesn't read it as didactic. "It's intensely political, of course, but not because it tells you how to live your life. I don't think Brecht does that, and if he did it wouldn't be interesting. When Mahagonny asks questions, they're open, not closed. You won't find much in the way of answers; and that's partly why the piece is so bleak. The city ends up damned and destroyed. You don't exactly get a feel-good ending. But at the same time, it's so relentlessly about the evil of modern life and money that I've come to feel the whole thing is really about God and love - who feature by their very absence. It's like Gulliver's Travels, where the text is so weighted toward the negative that it actually implies the positive. If that makes sense."
It does. Especially when you know that Donnellan is a practising Catholic, with specific views about another subject that he finds at the heart of Mahagonny. Choice. "We live in a time where choice is thought to be good, and under a government dedicated to giving us more of it. But choice can be a terrible god, because the more things you can choose the harder it is to see what really matters. I'm not saying we shouldn't have it: just that it's a distraction and not necessarily the cure-all that ad agencies and the characters in Mahagonny tell you."
What Declan Donnellan tells you is born out by the example of his own life. As a stage director he makes choices all the time - "and after a day of working out who stands where, does what, and how, I'm drunk with it. I go out for a meal in the evening and give the menu to someone else. I've had enough deciding." But he has very deliberately limited the options on who he works with. Cheek by Jowl is a recognisable family enterprise involving much the same group of people: every production Donnellan has ever done has been with the designer Nick Ormerod, who is also his long-standing offstage partner. Meeting years ago at Cambridge, they both studied for the Bar, gave it up, co-founded Cheek by Jowl, and now cohabit in creative institutionality in Hampstead.
"We have a terrible working relationship because we don't have proper meetings. We just argue over breakfast. But it's the only way I know how to do things; and no, I don't see us going stale through over-involvement. The theatre is far too promiscuous. The best work I've ever seen has come from those Russian ensembles where everyone's been together for 20 years. That's my ideal. I wish there were more stable coordinates in my life, not less."
Does Ormerod feel the same?
"Well, he does sometimes work with other directors - the bastard - and was asked to do something for Peter Brook this summer. But when the dates changed and turned out to clash with Mahagonny he turned down Peter Brook for me. That was very loyal of him, don't you think?"
! 'Rise and Fall of Mahagonny': ENO, WC2, 0171 632 8300, from Thurs.