The Clerks present Cry God For Harry: Music from the Court of Henry V, in The Quire, York Minster, tomorrow night

"It's exciting for us," says director Edward Wickham. "It adds a certain frisson and presents an extra challenge because the music is quite dense and the text can be complex, and hearing it on the radio is a different experience.

"It means we need to be thinking about how we 'spatialise' the singers [in other words utilise the space for the six vocalists]. This is not flashy Renaissance music, but profoundly beautiful, though not in the ethereal, transcendent style. This is more like chamber pieces."

Cry God For Harry: Music from the Court of Henry marks the 600th anniversary of the Battle of Agincourt with a programme of music associated not only with the royal court but with the battle itself, in the form of English polyphony in the Old Hall Manuscript and from other early 15th-century sources.

Performed already in Durham, now in York tomorrow, and with two more concerts to come in Oxford and Cambridge around St Crispin's Day in October, the music operates in the service of religion, politics and ceremonial occasions. "In putting the programme together, we started with the music specifically associated with Agincourt, so the first piece you go to is The Agincourt Carol, which tells the story of the battle; then the triumphant procession conducted into London and other music associated with that," says Edward.

"Then, more widely, we opened it out for music that we're pretty sure was commissioned for the chapel of Henry V and a couple of pieces that are attributed to Henry V himself, though whether he actually composed them, or someone did it for him...it's rather like Henry VIII and whether he wrote Greensleeves."

What's your hunch, Edward? "I suspect Henry V could have composed something; something that any cultured amateur musician could compose, but the Gloria we sing is more complex, and I'm not sure the raucous, fun-loving Henry we see as a prince in Shakespeare's Henry IV plays would have sat down long enough to compose it."

The Clerks have enjoyed a long association with the York Early Music Festival and Edward is delighted to be participating once more. "This festival was one of the first professional gigs we did, I would say in about 1995/96, and Delma [administrative director Delma Tomlin) has always been a great supporter of The Clerks and indeed of many of our contemporaries, so it's been a 'cantus firmus' of our life. We've been involved in the festival six or seven times over the years.

"The York Early Music Festival is one of very few in Europe that really has a reputation such that audiences can go to a concert with confidence even if they don't know the repertoire. It's one of those festivals with a title where you can absolutely trust the programme, so I would name York and Utrecht as the two most significant Early Music festivals in Europe."

As part of The Clerks' visit to the 2015 festival, with its focus on Anglo-French relations through 300 years of music-making, Edward will hold a free question-and-answer session at Bedern Hall tomorrow afternoon at 5pm. "It was me who requested it, for two reasons" he says. "One, because the music lends itself to such exploration as it's rather dense and the lyrics need some unpicking, and the listener's appreciation is helped by some foreknowledge.

"Secondly, because I'm also conducting some research at the moment, on how much text we hear in this kind of polyphony in a concert. I have the text set up where people will be asked to fill in a questionnaire to say what words they're hearing in that text because of the way it's being delivered by the singers.

"I think we assume as performers that we articulate very clearly at all times and the audience must hear everything, but in fact they don't."

The Clerks present Cry God For Harry: Music from the Court of Henry V, in The Quire, York Minster, tomorrow at 7.30pm. Box office: 01904 658338 or ncem.co.uk/yemf