Moved by the tragedy behind Berlioz's Troy story

"Convey my passion..." muttered David McVicar in his delicious guttural Glaswegian accent, blue eyes boring into mine, as we parted. Opera director David McVicar's passion is conveyed through opera. Each and every one of his productions never fails to hit his audience squarely between the eyes, its story as crystal clear as water in a burn. If you're a seasoned punter, experiencing a David McVicar production is equivalent to getting that elusive joke, to the penny dropping: "Oh, that's what this opera is about. That's why Figaro is wary of the Count, why Hans Sachs in Meistersinger is in love with Eva, why Salome dances the Dance of the Seven Veils." For a newcomer, the clarity of his productions generates new fans. As he says, "A 16-year-old who comes to see The Marriage of Figaro has to understand the story, which is not a story about a car factory."

When we met, two weeks into rehearsals for the new production of Hector Berlioz's Les Troyens (The Trojans) at the Royal Opera House, McVicar is at his best, delighted to be working with Tony Pappano. "We're very similar because we both know that the bigger picture is created by getting the details right and the psychological reasoning for everything," and they're passionate about "Hector".

Les Troyens is Berlioz's greatest achievement but he died having only seen the last three acts. This in itself only serves to heighten the emotion of the piece and as McVicar says, "He sort of knew as he was committing it to paper, that he wasn't going to see it and it's so moving." Moreover, "the responsibility of The Trojans is to try and get it right. And so few people have managed to get it right. And it's because, as he was writing it, he knew it was this mad exotic dream to write this piece. So when you do the piece, you've got this responsibility to do your best for Hector. Because there's no way that you can love Berlioz's music without loving the man, without feeling his pain and without feeling how heroic he was. His voice is so individual. He doesn't sound like anybody else. And the opera-going audience has so few chances to see the work done complete like this."

McVicar is not only doing the piece in its entirety, four and a half hours hours of music, he's also sticking to Berlioz's instructions in the score. "We're being pretty religious about stage directions. When you read the score, you see how the music is timed to things in his imagination."

To date, McVicar has delivered brilliant productions of the big epic operas. Will this be his greatest challenge so far? "Meistersinger is a huge challenge. It's just The Trojans doesn't get done as often as Meistersinger. I've done three years of preparation – Virgil, Greek myths. The score is that thick," he spreads his large hands wide, "and I've got to have it all in my head. I've done massive amounts of research on the Trojan war and have urged all the singers to read their Virgil."

Directing, he says, is synonymous to steering a ship. "Everyone knows they're going to be taken on a journey and the captain knows where the hell America is. That's what a good director does – he can steer the ship – and if I can't actually spot where America is, I don't let anyone know," he smiles.

'Les Troyens', Royal Opera House, London WC2 (020 7304 4000; roh.org.uk) 25 June to 11 July; and at BBC Proms, Royal Albert Hall, London SW7 ( 0845 401 5034) 22 July