Book of the week: The Divine Comedy, By Dante, translated by Clive James

A lifetime's practice of poetry equips James, as translator and interpreter, to scale this summit

The three parts of the Divine Comedy – Inferno, Purgatorio and Paradiso - are an expression of faith undertaken to the glory of God, and a demonstration of the use to which God's gifts can be put.

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The poem's religious scope is matched by its influence. It is as important as its lineal ancestor, Virgil's epic Aeneid, which transports Homeric characters to Italy and thus to the founding of Rome. Whereas Virgil lent legitimacy to the Emperor Augustus, Dante, working in exile, offered a corrective to the many errors of the church, serving God rather than the corrupted secular power of Rome. It would be hard for a poem to be more culturally significant, and such a role and status would be unimaginable now. As Seamus Heaney remarked, Dante seems to be writing "on official paper".

Such is Dante's greatness that the dying-away of the Catholic theology he dramatises in the Divine Comedy does nothing to diminish his attraction for poets, translators and other readers. As Shakespeare is to drama, so Dante is to poetry: a star shedding light everywhere. Of the poem's three parts, the Inferno is the most popular. Hell seems of particular interest in an unbelieving age, perhaps because it offers a structure in which to contemplate folly – and also contains the most interesting characters. In comparison, the road to paradise can seem less compelling. Clive James seeks to correct this imbalance.

Translators approaching Dante must make some formal decisions at the outset. Will they try to reproduce the poem's terza rima, the ever-moving ABABCBCDC etc rhyming tercets? Eleven syllables? Iambic pentameter, rhymed or unrhymed? Free verse? What of the poem's decorum, its dignity, its presiding tones? How to make a version neither anachronistically modern nor fake-medieval? And will there be line - or at any rate stanza- equivalence between the original and the translation?

Clive James comes to the Comedy with two important attributes: many years' study of the poem, and an impressively accomplished verse technique. That technique has sometimes outgunned his own poems, as if he has needed a greater sense of friction with his material. In scale and difficulty, the Comedy presents a suitable challenge, and hearteningly it is sound as much as sense that concerns him.

James writes in iambic pentameter, with full masculine rhymes throughout, and in rhyming quatrains rather than tercets. And he takes the further liberty, implied by this decision, of adding length to the original. For example, the 136 lines of Inferno Canto I become 173. He argues the case for this in his introduction: why should historical obscurities forbid the reader? People have probably been hanged for less. The reader who reads Dante is also capable of reading notes, or we are doomed.

The actual results include interesting interpolations but perhaps shed less new light than James supposes. In a note on the translation, Dennis Looney, scholar of Italian adds, "Anyone comparing this translation with the original may wonder at times why Dante didn't do this himself." Anyone? Speak for yourself. Looney seems to have no idea how poems are written. Dante wrote the poem the imagination gave him to write. Clive James's good friend, the late Peter Porter, greatly disliked Dante's world, but he would have roared with laughter at this barmy displacement of art by convenience. Not for the first time, Randall Jarrell's anecdote of the pig turning up at a bacon-judging competition comes to mind: what, the pig was asked, could it possibly know about bacon?

James, on the other hand, is a bacon expert. He can muster the powerful plainness which is so important to Dante, as when he turns on Florence, the birthplace that betrayed him: "Florence, rejoice! For you are grown so great/ Your wings beat proudly over land and sea,/ And even Hell proclaims your rich estate." The rhyme is exact, bitter and widely resonant. James also successfully negotiates the nightmarishly vivid set-piece where men and snakes are transformed into each other. He is emboldened to take a tonal risk at the end of Ulysses's account of his last, forbidden voyage beyond the Pillars of Hercules: "Three times the waters led/ Us in a circle. Fourth time, out of luck./ Stern high. Bow low, we went in. Overhead/ Somebody closed the sea, and we were dead."

Whatever the reservations about the addition of material elsewhere, these episodes are compelling as the verse versions of scholars often fail to be, because James keeps the poem as poem uppermost. It's no use if the English version doesn't move and ring like a poem. The best of James's translation has a propulsive, urgent energy that finds a clear course through Dante's extended similes and his equally extended history lessons.

There are problems, though. He is too fond of verb contractions and of the merely contemporary phrase - "top-down", "This isn't real", "Heads up", "cosy perks", and so on, which recall the glib facetiousness of some of his other work. At times too – and James is by no means alone here – the control of tone, idiom and sentence structure slips, and from speakable English we move into the special purgatorial zone of translatorese.

Translators also like the Inferno because it's full of objects, places and physical activity. By the time Dante is guided by Beatrice into Paradiso, the poem is fully airborne and the poet has to deal with a series of minutely-described visions composed of light, colour and space, where history, theology and cosmology meet and are assumed into the final sight of the pulsing rose in which the Creator's love timelessly embodies itself.

Here the particular and the general, past, present and future, mystery and revelation, free will and fate, are resolved in the permanent fact of divine attention and, in TS Eliot's phrase, "the fire and the rose are one". James handles the challenge with urgency and conviction: what is "Bound in one book by love" holds the imagination as more than a distant report. He closes with a beautiful diminuendo that seeks to magnify all it cannot express: "now, just like a wheel/ That spins so evenly it measures time/ By space, the deepest wish that I could feel/ And all my will, were turning with the love/ That moves the sun and all the stars above."

Sean O'Brien's poetry collections have won the Forward Prize (three times) and the TS Eliot Prize