Reading Andrew Motion's lucid, brilliant, melancholic poetry collection The Customs House I was reminded of Edward Thomas's moodily captivating essay "One Green Field' in which Thomas realises how "Happiness is not to be pursued, though pleasure may be; but I have long thought that I should recognize happiness could I ever achieve it ... I never achieved it, and am fated to be almost happy in many different circumstances ..." The Customs House is a strong, searing and sad book. I think it is certainly Motion's most achieved collection. It signals a central change to the way he is thinking and feeling in language. He is letting the world back into him. Not the public world and restive politics of the laureateship, but a private world of understanding, humility and love. Motion is developing a late style that is far more open to possibility, one that is "almost happy in many different circumstances":

The last colour to see when the sun goes down
will be blue, which now turns out to be not
only one colour but legion  as if I never knew.
("Gospel Stories")

Edward Said believed the late style of creative artists "is what happens if art does not abdicate its rights in favour of reality". I would argue (and I have heard the poet state as much) that Motion's stint as laureate pushed him to abdicate the rights of his poetry to the reality of that public responsibility. Writing of the final poems of Cavafy, Said commended "the artist's mature subjectivity, stripped of hubris and pomposity, unashamed either of its fallibility or of the modest assurance it has gained as a result of age and exile". The Customs House possesses and is possessed by a bare, pared-down tone stripped of hubris and unashamed of its fallibility. Motion has fully returned from the public exile of self-conscious art. He returns scorched but wiser. As with the line of English poets  Thomas Hardy, Edward Thomas, Keith Douglas, Philip Larkin, Motion himself  the mature subjectivity of tone is of course a never-to-be-realised happiness, a restlessness of feeling, a scarred understanding that yields fine, heart-rending language and the grace and pressure of precise memory:

Now wind has died in the lime trees
I have forgotten what sense they made,
but not the leaf the wind dislodged
that fell between my shoulder blades.
("Fall")

Motion's poetry has always possessed an affecting tonal vulnerability. It is a quality that draws a reader closer  as does his famously hushed presence when he reads in public. It is a silence made of unwritten sentences. Almost (but not quite) of self-annihilation. Yet it is also the brilliance of concentration in which both tone and image lean into each other without falling, and hold each other and proffer some slight consolation. Like his hero Edward Thomas, Motion can create images and tones of such word-carried, world-wearied sadness that you accept their truth while simultaneously believing in their fictive grace. Truth and beauty: those dissimulators. Motion used to be their master. But in poem-sequences such as "Gospel Stories", "Whale Music", "A Glass Child" and "The Death of Francesco Borromini", he is now  in his late style  humble before them. He has served his term.

Is the music of his poetry as finely judged as the tone? The first section of this book is something of an experiment. It comprises a series of war poems. These are "found poems"  which is to say (Motion notes) "they contain various kinds of collaboration". The collaborations find their origins in oral and written reportage, and in war-time stories from veterans of the world wars and the recent and current conflicts in Iraq and Afghanistan. For example, in "The Golden Hour" (which refers to the time during which a traumatised patient has the best chance of survival), an army surgeon addresses the reader: "For instance: one patient I remember had been in a blast situation / with no visible injury but we were not ventilating very well at all. / I put two openings in both sides of his chest with a big scalpel blade; / then I could stick my fingers in, and knew his right lung was down / because I could not feel it. However, I was now releasing trapped air / and the lung came up again. He has responded within the golden hour."

"Because I could not feel it." The verbal truth of the war poems is fascinating in that their poetic music is almost completely surrendered in order to honour the spoken clarity of factual experience. This requires a sensitive ear for line-break. Some of the material swings close to the prosaic, yet Motion's deft lineation and deletions work double-time to preserve the true sense of natural speech. And Motion is generous as a translator of experience. He allows the hard-won details and voices to carry their own poetry. The voices of the war poems shift from the panoptic to a microscopic focus. Tight scenes possess intense light and energy. There is no desire to press a bright-red antiwar poetry button; no call for the trickery of literature; and no call above the quiet truths and sensibilities of those on the front line. In terms of poetry and in terms of truth, The Customs House is an honourable, humbling achievement.

 David Morley's Enchantment is published by Carcanet.

"The Customs House"  the title poem  is a tease with its suggestion of dues to be paid on "merchandise" and the last-minute sighting of a man labouring with a chest of drawers who seems to relieve the poet of any obligation to come forward with something  or nothing  to declare. The baggage-handling in this collection is adroit. But what sort of a reckoning is going on?

It is Motion's first collection since he retired as poet laureate and is divided between accomplished performances about war and more autobiographical offerings. What the poems share, on all subjects, is an artfully relaxed, well-groomed quality. Not easy to achieve, one assumes, and yet, for the reader, sometimes tantalisingly withheld.

What Motion does with war poetry is akin to what Sebastian Faulks pulls off in some of his novels. There seems to be a compulsion for certain men of a post-war generation to write about fighting almost as a literary substitute for active service. But the relationship to past wars for a writer is complicated. Motion may lack the front-line authority of a Wilfred Owen but he has another weapon: hindsight. This is deployed with skill in "Laurels and Donkeys", describing the 11-year-old Siegfried Sassoon's childhood idyll of a picnic while also anticipating his death. Motion also looks back on his own childhood to salute his father who fought in France on D-Day. In "Now Then", he remembers being handed his father's "enormous boots" to polish: "There was no way I could ever make the toes brighter than they were already." Yet the collection is the poetic equivalent of exactly this: making borrowed boots shine.

There is a splendid elegy for the wonderfully named Harry Patch, who died at 111, in which Motion summons back the veteran's comrades: "hundreds of thousands of dead who lie there/ immediately rise up, straightening their tunics." It is a volume filled with revenants  a platoon of ghosts  from his father to the poet Mick Imlah, movingly remembered in "The Visit". The book leans towards the elegiac  poetic undertaking in every sense. But there are also attractive exceptions such as "Whale Music", in which Motion offers us a whale's eye view in a poem of marvellous gravity and caprice.

This is a collection that makes one think about how poems earn their keep and the difficulties involved in deciding who the best audience for a poem is. Some of the poems to his third wife, Korean interpreter Kyeong-Soo Kim, feel more like private shorthand than evolved work. I have been puzzling over a line about the shoes that were part of a love at first sight: "With that exciting ridge along their toes like a seam/ which is normally hidden but was plain for all to see." Army boots are perhaps easier to polish.Yet there is, in the same section, a beautiful and fully realised poem, "Holy Island", in which ravens are perfectly described as "weightless cinders" and, without labouring the point, his wife's black hair becomes part of the scene. The poem has an apt, assured ending: "The ravens swoop down and settle among the gorgeous pages of the gospels."

But more often poems end in a wilfully flat manner. Sometimes, this is a recognition that war encourages inarticulacy. He quotes in "The Vallon Men" a soldier: "We have lost a lot of friends/ And we have seen a lot of things that are not ideal." And, with that, the poem halts.