There's fun chemistry at work in Under Milk Wood. It's no surprise when you meet the team behind it, writes Belinda McKeon

To begin at the beginning - to steal the opening lines of Dylan Thomas's 1951 play Under Milk Wood - it is spring. Not a moonlight night in a small town, "starless and bible-black", but a bright April day in a south-western city, bustling with shoppers and not looking as if it has much time to consider the colour of bibles.

The place, though - in which actors Jon Kenny and Myles Breen are rehearsing under the sharp eye of Island Theatre Company's artistic director Terry Devlin - is a glory which might have stepped straight from the environs of Thomas's imagination. The little building which was once St Munchin's Church huddles in the shadow of a former Bishop's Palace, now home to the local Freemasons.

Brokenly circling the area, which is actually an island (King's Island) in the middle of the city, are the remains of old city walls and the tall ramparts of King John's castle, now defaced by a modern entrance. Through the gates of the long-deconsecrated St Munchin's, the way to the company's offices and rehearsal space is along a narrow churchyard crowded with the heavy stones of the dead. "Listen," wrote Thomas, in those beautiful first lines, "from where you are, you can hear their dreams."

Step into the old church, however - still lined by elaborate memorial plaques from past centuries, still lit through some lingering panes of blue-stained glass - and you'll hear the dreams of Thomas's villagers themselves. Or rather, the squawk, cluck and screech of Kenny and Breen as, perched on the edge of a table, they breathe life into those dreams, and into the complex lives of a sleepy village. Just now, they're First Neighbour and Second Neighbour respectively, lamenting the lot of poor Mrs Waldo.

Seconds previously, they've been Mrs Waldo and her gently snoring husband, all 17 stone of him; and before that, Evans the undertaker and Jack Black the cobbler and Miss Price the dressmaker and her lover Mr Edwards; and seconds from now they'll become Mrs Ogmore-Pritchard and her two dead men, and Organ Morgan, the organist, and Ocky Milkman, as he dreams of emptying his churns into the river.

It's time to take a breath, but they scarcely do; between them, Kenny and Breen are playing the 57 characters of Thomas's unforgettable journey through the unconscious minds of a little Welsh village on the sea, and, to watch, the chemistry through which they approach the task is utterly exhilarating.

Unsurprisingly, with these two actors on board, it is also frequently hilarious in its touches, in its interpretations, in its emphases. And in its errors. "Never work with marbles or animals," breathes Kenny, as an ambitious scene involving a rolling set of tiny glass balls goes pear-shaped for the fourth time in a row, Breen helpless with laughter behind the dark glasses of the blind Captain Cat as he attempts to control them. Devlin, too, can't help but crack up.

But they'll get it; slowly and steadily, the myriad nocturnal encounters of this village which has "fallen head over bells in love" are coming together.

Bearing the duty to share a narrator's voice along with those of several plays' worth of characters, the script can hardly have been a soothing sight for the actors in the first rehearsals. Breen imitates the startled gasp he emitted when he first read the script after being approached by Devlin. "Even if you had 18 or 20 people," he says, "it's an epic. It's a big, rich piece. How do you get your head around it?"

Though he has been familiar with the play since first seeing Andrew Sinclair's 1971 film version (after which he went to the script, which he "much preferred"), Devlin agrees that the initial encounter can be a daunting one. All three say that what makes the process a relatively fluid one is the startling depth and beauty of the language.

Written just two years before Thomas's untimely death at the age of 39, Under Milk Wood is a breathtaking symphony of voices as quirky as they are quaint, as unsettling as they are innocent, and the lines in which they are expressed leaves little doubt as to their author's status as a poet of major importance.

"The thing is," says Devlin of the early challenges of staging the play, "once you start reading it aloud, the characters just come. That's how good the dialogue is."

Breen agrees. "I mean, it is sort of - those words in your mouth - it is sort of like Shakespeare. The richness."

One of the things Kenny found as the actors moved away from dependence on reading the script ("says he," he laughingly chides himself, referring to the occasional glitches in the morning's rehearsal) was that the play - although originally written as a radio play, hence merely for voices - contained everything they needed to bring an entire world alive.

"When we got it onto the floor and started to move it around," he remembers, 'for something that had no set design, no floor plan, that was a blank piece of canvas, one of the amazing things was that we just found ourselves naturally getting into positions, our bodies . . . it was amazing how easily it sort of transported itself onto something visual. And the characters moved as well. Like, when he does give a hint, you know, it's quite physical, and I think Myles and myself are playing it quite physical as well, like when we both play Mr Waldo, because he's 17 stone, at certain times we deliver his lines in chorus."

Whatever about both playing the same character at the same time, the actors are still grappling with the task of playing the full gamut of Thomas's characters, of moving seamlessly between lines and lives. Once again, says Breen, it's the language which allows them to do this. "It's sort of an organic process," he says. "To colour the poetry with the two voices. I mean, we're still fine-tuning on who says what, and there is a sense that it's about the feel of it, more than about, oh, I learned my lines, and don't give me any more!"

The question of who says what has changed several times since the script was first brought into rehearsal, says Devlin, and in a sense this is the advantage of having a relatively unstable text; during the last days of his life in New York, in November 1953, Thomas was still making cuts to the play, still hoping to see it gain a life beyond the airwaves, and the work of the successive editors who have attempted to shape it into such a life has lent to Under Milk Wood a degree of flexibility.

But, says Devlin, the heart of the play remains unchanged since Thomas's day. Despite the shadows of darkness the writer's suggestion of a ghostly air can throw over the play - or indeed, which can be cast by the tragedy of his own short life, by the sense of the author himself as a ghost in their midst - for Devlin, this is a play about the joys of new life . . . and the joys of bringing such life about in the first place. "The damn town", he says, "is obsessed with sex. And the play is absolutely a celebration of spring. And of recreation and reproduction, and the energy of that is what flows right through the play. What is Gossamer Benyon doing when he says that she's ferretting beneath the sheets? When Nogoodboyo is up to no good in the washhouse, what's no good? And, while he never actually mentions this force that drives the green flowers, as he puts it in a poem, yet it permeates the play all the way through."

The happiest characters in the play, says Devlin, are those who sit somewhat at ease with the fact of themselves as sexual beings. "I think that he celebrates the way that people, even under the heel of a more puritan time, just find ways of getting out and expressing their sexuality and their warmth and the joy of it."

This is not a joy (or a struggle to admit joy) likely to be found only in a 1950s village such as Laugharne, where Thomas spent his later years, and widely believed to be the inspiration for Llareggub. "It most definitely could be a village in Ireland in the 1950s," says Devlin. And in the present day? Breen and Kenny nod vigorously.

All the same, this relevance might seem ambiguous; Kenny's enunciation, in particular, has traces of the Welsh accent with which Thomas's language is flavoured. "I kept a little bit of it, I think," he admits, "It sort of lends itself. There's probably a thing in it, though, that reminds me of something like a Cork accent; there's a sing in it, a rhythm in it."

Yes, says Devlin, that can be a danger: "A lot of Irish people who start doing Welsh accents end up in Cork."

But the closeness of the lilting sounds is something with which he's not unhappy. "We thought if we played this thing heavily in Wales," he says, "then what we would have would be a play that became an object, something in the distance, so we're trying to blur the boundary between Ireland and Wales. Yes, there's a blas of the Welsh accent here and there to the play, but essentially, we're trying to soften that. So that people don't think that it's just over there. So that it could be happening here."

Watch Kenny, as mother, boxing the ears of Breen, as schoolboy; or Breen, as harlot, flattening the ego of Kenny, as frump; or both of them, together, intoning the scrambles for news of two gossiping neighbours; and of that much, there can be no doubt.

Under Milk Wood is previewing in Tipperary Excel until tomorrow, and runs in Glór, Ennis Apr 12-16; Pavilion, Dún Laoghaire, Apr 19-23; Dunamaise Theatre, Portlaoise, Apr 26-27; Backstage Theatre, Longford, Apr 28-30; Belltable, Limerick, May 16-21