Whatever other qualities composer John Metcalf might possess, he’s certainly not short of courage.

Making an opera out of Dylan Thomas’s radio play for voices, Under Milk Wood, in the poet’s centenary year, would strike some as foolhardy, not to say sacrilegious.

It’s not the greatest piece for radio ever written but it’s probably the most original in a medium with its own rules.

Metcalf, instead of basing a libretto on Thomas’s script, uses the words themselves to create an original work that contrives to be both faithful to the play and a piece of sustained musical invention.

Keith Turnbull’s production employs Canadian and Welsh forces - eight singers and five musicians, all under the keyboard direction of MD Wyn Davies and cleverly occupying the stage as if it were a broadcasting studio. Indeed, it’s exactly what a radio performance of the work might be like to watch, bar a few background visuals and a certain amount of choreographed movement navigated around the central seated figure of Michael Douglas Jones as Captain Cat, he of the regurgitating memories.

Metcalf constructs 29 short scenes, each associated with a musical key and ending cyclically in a positive C major. The method’s not unique in opera but, lacking the genre’s dramatic tensions, it does suggest that his Under Milk Wood is more akin to a theatre piece performed musically than an opera proper. Sound effects both pre-recorded and created on the spot are skilfully incorporated into the score.

At the start, the audience might be concerned that their reservations are about to be justified, because the opening of Thomas’s script is among the most familiar in modern Welsh literature. To hear those words sung might sound odd, and unlike the musical setting of well-known poetry.

Metcalf, however, soon establishes a lyrical idiom in which the words, actions, thoughts and voiced opinions are at home. From then on, settled into a form which needed to be convincing, the goings-on enter another dimension and are no worse for it.

He’s blessed with a cast - sopranos Elizabeth Donovan , Helen-Jane Howells and Gweneth-Ann Jeffers, baritone Paul Carey, bass-baritone Jones, mezzo Karina Lucas, tenors Richard Morris and Eamonn Mulhall able to take advantages of what are often ‘operatic’ set pieces, especially the monologues, which are treated in an unabashed arioso style. Flautist Jose Zalba, strings-player Parmela Attariwala, harpist Deian Rowlands and percussionist Paul Stoneman become part of the stage wanderings. Even Wyn Davies is all-action, singing as well as playing keyboards and conducting.

The only reservation is the way a musical setting sometimes blurs the words - in this work, the words are everything. Otherwise we are offered an effective and affectionate transposition of a Welsh classic. The cast had its measure from the start and what could have been too busy a stage scenario turns out to be eminently watchable. Why the show isn't being presented in London is a mystery. Dylan Thomas and Under Milk Wood go beyond a purely Welsh dimension, as does this terrific production.