They were both brought up in Swansea and they are both Welsh poets. But there the similarities between Dylan Thomas and Dr Rowan Williams seem to end — the one careering headlong through the bars of South Wales, London and New York, where he met his untimely death half a century ago; the other taking a more considered route, winning a scholarship to Cambridge and becoming Professor of Divinity at Oxford before being enthroned as the 104th Archbishop of Canterbury last February.

However, as William Blake noted, the road of excess can lead to the palace of wisdom, and there are critics who regard Thomas as a great religious poet. From early meditations on death and the universe such as Before I Knocked, through swirling anthems like Ceremony after a Fire Raid and paeans to nature as simple as Fern Hill, down to the more pronounced liturgical symbolism of This Bread I Break , Thomas gives a sense of something far more deeply interfused.

The source of this spiritual awareness intrigued me when writing my recent biography of Thomas. His own rackety lifestyle gave few clues. Was it something to do with Welshness or perhaps an integral part of being a poet? I jumped at the chance to discuss these matters with Dr Williams, whose most recent collection of poems appeared last year.

We talk in front of a lazy gas fire in the Archbishop’s book-lined study in Lambeth Palace. Limpid afternoon sunlight floods in through leaded windows that overlook a well-tended garden. The Archbishop’s delight in Dylan Thomas’s poetry is immediately obvious. Like many people, he latched on to it as a teenager, discarded it, then rediscovered its virtuosity.

His early passion was for “a poet whose energy goes very much into the physicality of things: it’s ideal for the adolescent hormones and it has a very bad effect on adolescent writing”. By way of explanation, he adds in a clear, modulated voice: “All adolescents want to write miserable poems about not being understood and about the nature of God and sex and death. Dylan makes you think, ‘Oh I can do that.’ Fairly soon you realise you can’t and then you begin to see what the labour’s about. One of his extraordinary skills is to lure you into the ease of it — the memorable phrases, the musicality, the physicality — so you don’t notice the labour.”

I remind him that, for all the attractions of technical skill, especially to fellow poets, the public usually wants some substance, some meaning. Here the Archbishop draws on his (and Thomas’s) Welshness to explain how meaning can emerge from formal structures, such as classical Welsh poetry, with its strict metres and systems of assonance and alliteration, which Thomas clearly, if unconsciously, drew on.

As for Dylan’s religiosity, he suggests that, like Geoffrey Hill in his early poems, Dylan’s exact relationship to belief is uncertain but, nevertheless, he simply cannot stop himself viewing things from a religious perspective. Although not quite a Christian poet like his friend Vernon Watkins, Dylan was “someone moving in and out of” the Christian tradition — “soaked in it, loving it, pushing back at it”.

One bonus of being Welsh is this twin heritage of formal verse and religious culture. It also means belonging to a nation that honours its poets. Dr Williams points out that the annual Eisteddfod remains “perhaps the best-attended cultural festival in Western Europe”. Its proceedings are conducted in Welsh, which, significantly, “is not a language which has evolved in the cosmopolitan worlds of commerce and industry. There is something about writing in Welsh that tends to drive you to the elemental.”

The Archbishop is not unaware of inherent problems, such as younger Welsh poets wanting to articulate “much more complicated contemporary experience”. But how can this be achieved without the “McDonaldisation” of the language? “Do you just want Welsh to be a vehicle for the same dreary global culture?”

Such considerations seem distant when he talks of his aims in his own poetry. “Basically it is a verbal rendering or translation of some coming together in perception. Sometimes these are ideas, but ideas make bad poetry. More often they are images, or the superimposition of one impression on another.” Quoting his Windsor Road Chapel, he recalls how the combination of soft carpeting and wood behind the pulpit reminded him of airport departure boards and cinema screens.

Does he try to convey a Christian message? “My instinctive answer would have to be no. I’m a Christian trying to write poetry, and that of course affects what I write. But I quail at the thought of sitting down and writing poetry with a Christian message to it. Poetry or novels with a Christian message generally are terrible.”

Although, with due modesty, he recently put himself at “number 57b” on the list of Swansea poets, he believes poetry has a role in combating secularism, which he decries for “stripping away a dimension to what you see” rather than simply for denying a religious frame of reference.

This idea requires a sophisticated Christian sense that everything has already been observed by someone else, and in particular by God’s love. The Archbishop likes to quote from T. S. Eliot’s Burnt Norton: “And the unseen eyebeam crossed, for the roses / Had the look of flowers that are looked at.”