In 1937 a Marxist Edgell Rickword took the measure of a Marxist W.H. Auden in a short essay, 'Auden and Politics'. 'The subject of his poetry is the struggle, but the struggle seen, as it were, by someone who whilst living in one camp, sympathises with the other; a struggle in fact which while existing externally is also taking place within the mind of the poet himself, who remains a bourgeois.' Auden turned thirty that year. He was preparing to 'wester', to leave Marxism ('the lie') and England and his readership behind, abandoning one source of energy, an ideology that helped displace some of the tensions and obsessions that belonged to the camp he lived in. Departing, he freed complex personal energies, which were to find their own ways with form, diction and theme. He began to refigure his past and move on with altered finger posts.

On his sixty-fifth birthday BBC Radio broadcast a celebration of his work introduced by George Macbeth. He wished the poet, recorded on what sounds like a congested and airless day in New York, 'many happy returns in two senses': over half a life later, and with a very different oeuvre to his credit from the one he set out with, Auden came to rest at Christ Church, Oxford, rather as E.M. Forster had found refuge at King's, Cambridge. Here he found himself. 'The old Greeks got it all wrong:/ Narcissus is an oldie,/tamed by time, released at last/from lust for other bodies,/rational and reconciled.' But not too rational. 'Sing, big baby.'

The British Library published a pair of CDs to mark Auden's year, an irresistible addition to any iPod or sound library, and a wonderful way to round out his centenary, so widely and imaginatively marked throughout the world. The CDs include the sixty-fifth birthday reading: stunned, exhausted, yet enchanting.

Travelling back from his hundredth to his thirtieth birthday, whom do we find? Some readers still see early and later Auden as different people and prefer the purposeful to the picaresque man, the public voice to the lucid and often appalled witness to human history, the human condition and himself. In 1937 he was the poet of his generation. He had visited great human upheavals; his poetry reported on modern history, on geology and nature, interpreted from specific perspectives, his diction enriched by the language of science and politics. His vision had an intransigent if sometimes a rueful heart. From this vision were absent some of the strains that sounded in his earlier verse, and that would find their way back into his writing as the quixotic chapters of his life succeeded those of radical engagement.

It is less the young than the mature Auden who left his print on later writers. His intellectual and formal impact has been as wide as Wallace Stevens's and sometimes, paradoxically, continuous with his. This has to do with the ways in which both think through poetry, moving towards an area well out of range of paraphrase; and how they are able to deploy abstract words that draw solidity from their formal context; and how they master their different prosodies. Stevens comes first, then Auden follows.

A double issue of the magazine New Verse was dedicated to Auden at thirty in 1937. There Rickword dissented; so did a few others who at once admired and resisted Auden. Allen Tate noted his and his friends' 'juvenile' and 'provincial' perspectives, the conspiratorial nature of his ascent to fame. Dylan Thomas offered his famous barbed tribute. 'I think of Mr Auden's poetry as a hygiene, a knowledge and practice, based on a brilliantly prejudiced analysis of contemporary disorders, relating to the preservation and promotion of health, a sanitary science and a flusher of melancholia. I sometimes think of his poetry as a great war, admire intensely the mature, religious, and logical fighter, and deprecate the boy bushranger.'

'Brilliantly prejudiced analysis': he speaks for but also speaks beyond a cause, and hence can move, and move away, when analysis fails or is disproved. The contemporary disorders were at the time political, but underlying those were the disorders that Freud and not Marx might address, the disorders that released him from his service to a prescribed programme.

During Auden's centenary year many new readers discovered him as a writer whose challenge remains fresh, whose place in the history of Anglo-American modernism is, despite his more vigorous fulminations, decisive. Does he affront his engaging youth with his cantankerous age? Is the opinionation of the Marxist more palatable than that of the mature poet, cantankerous, a hoary-headed Narcissus wrapped in the wry embrace of self?

At the end of his centenary Auden is better known than he has ever been, and better loved. The rift that his contemporary and later critics opened in him, between Marxist and Freudian, young and old, English and American, has begun to heal. He is of a piece, the trajectory of his work shadows the poetic and political trajectory of his century. There is an abundance of wisdoms in Auden; the late poems surprise with their rightness as often, as deeply, as the early ones do.

Another birthday, differently momentous, was celebrated in 2007, that of the Poetry School, now ten years old. Established by Mimi Khalvati and a few others in the last millennium, it is based on the archaic notion that writing poetry entails the acquisition of skills - including reading skills - and the mastery of the medium through study and practice. It began in London and is now active in many parts of the United Kingdom. Several events marked its successful first decade, the last one being a round table discussion with Eavan Boland, Robert Potts and Germaine Greer on the theme proposed, then qualified, by Auden: 'Poetry makes nothing happen.' Clearly his centenary, and the Poetry School's birthday celebration, are evidence to the contrary.