A stage production is a chaotic affair in its early development. No surprise really, since the point of workshops is to try ludicrous things, see if they work, and bin them if (mostly when) they don’t.

On paper at least, there’s scarcely more risky an idea than choosing a mute animal as the central character of a stage play, as War Horse does. But what emerged from its early workshops in 2007 was enough of a viable idea – a tantalising hope – that something unique was possible.

What does a composer do at such a workshop? In my case, not very much actual writing. My job at that point was to try ludicrous things myself. Like the rest of the creative team including the show’s ‘songmaker’ John Tams, I needed to grope around in the dark for a bit – getting a sense of what did and didn’t work, and what the musical language of the play might be.

A good way to start that process is with some blatant misappropriation. I raided the chest of early 20th-century orchestral literature for a wide range of different material: passages from Stravinsky, Mahler, Vaughan Williams, Walton, Berg and others. Then the rough outlines of scenes that our actors were fashioning - battles, village celebrations, intimate emotional transitions - were pelted with these random chunks, triggered over loudspeakers in the rehearsal room. Partly, this revealed the music’s stylistic relevance (or lack of) for a scene, but its more important effect in many cases was to suggest hidden things about the scene itself and the emotional states of its characters that we couldn’t otherwise have premeditated.

As the picture formed in our minds of what we were doing, this scaffolding was gradually removed and development of the original score began, firing up its own internal engine in symbiosis with the dramatic language and arc of the play.

One of the principal lines of that arc in War Horse is descent into trauma. Peaceful, harmonious pre-war village life transforms into the brutality of the trenches. The music’s development reflects this change; beginning in a world that echoes Vaughan Williams, the score gradually transforms into something that, at its extremity, becomes Stravinskyan barbaric mechanism representing the battlefield tank. This transformation is reflected too, in Rae Smith’s design for the show, with her stunning drawings moving from rich Devon landscapes to shattering Vorticist abstracts.

It was evident from the beginning that the score for War Horse needed a cinematic conception, with an epic orchestral sound. Without the physical room, let alone the budget, for an 80-piece orchestra in the theatre every night, the score had to be rendered (as with much film music) by a hefty dose of studio technology.

However, in 2010 when the show’s success and reputation was well-established, progressing the score to a live concert platform seemed a logical choice. I began work on a 20-minute piece, entitled War Horse Suite. In the concert hall, this piece had to stand on its own feet from a musical drama point of view, since its role was no longer one of subservience to something else. So I chose to rebuild the score from the ground up as a one-movement symphonic poem that loosely retells the story of the play in its own musical space; maintaining dramatic tension, without being bound strictly by the play's narrative.

Later, the idea was floated of an evening-length event in which Michael Morpurgo would read the complete book on stage, accompanied by an orchestra, chorus, and projections of live drawings by Rae Smith. And so, War Horse: The Story in Concert was born. It had its first outing in the Royal Albert Hall in October 2016.

The musical format of this work is more closely related to that of the original stage show than is War Horse Suite. It returns largely to the individual cues from the show, but I had the opportunity to enhance, refine and extend the musical line and the orchestration detail.

When the chance came the following year to record this new work at Abbey Road Studios with the RPO under David Angus, and with Michael Morpurgo himself and Joanna Lumley narrating, I was thrilled. It’s what I consider to be the finest embodiment, by world-class musicians, of the original conception of the show’s music score.

War Horse: The Story in Concert has been re-released on CD and vinyl by BMG. It is narrated by Michael Morpurgo and Joanna Lumley. For more information, please visit: warhorseinconcert.com