It was in the mid-1970s, sitting in a house in a remote Donegal townland, when I first saw an edition of The Late Late Show. After half an hour or so watching Gay Byrne alternately pursing his lips, winking at the audience and lavishing praise on his guests, I asked my hosts: "Is it always like this?"

"Like what?"

"Well, he's so full of himself, so unctuous, so bloody condescending. The interviews run on and on - and those blatant commercial plugs!"

To my cynical British eye, attuned also to the relative slickness and fast pace of British and American television, it appeared rather quaint, a little - dare I say it - provincial and definitely old-fashioned. My friends were genuinely baffled. I would need to see the programme regularly, they said. This wasn't a good example. I didn't understand Gaybo's significance, the risks he took, the way he often dared to assail Ireland's sacred cows.

They were willing to concede that Byrne could be infuriating on occasions, but so what? The positive far outweighed the negative. Their passionate defence of what I misunderstood to be just another chat show was revealing in itself. Byrne was not a Johnny Carson nor a Michael Parkinson. Celebrities did appear on The Late Late Show but that wasn't its raison d'etre. It dealt with real issues and featured real people. It mattered. It couldn't be ignored.

It took some time for my scepticism to fade until I came to an understanding that the phenomenon that is Gay Byrne is embedded within Ireland and its society. His show couldn't be exported and it is impossible to compare it with any British programme.

At various times there have been seminal TV series in Britain, such as That Was The Week That Was, Monty Python and Til Death Us Do Part, but their influence has been diffuse. No current affairs programme, not Panorama, not World In Action, not Newsnight has ever consistently set the national agenda in Britain. By contrast, The Late Late Show has been at the epicentre of the ongoing debate about values and morals in Ireland's rapidly changing society ever since the 1960s.

Though I have never quite overcome my dislike for the sickly sugar coating of Byrne's showmanship, down the years I have come to appreciate that he has been a sort of social revolutionary, a subversive undermining the oppressive foundations of the quasitheocracy which marked the first 40 years of the State.

I find myself in total agreement with a number of the more sensible commentators - such as John Ardagh, Fintan O'Toole and Finola Doyle O'Neill - who view Byrne as a catalyst for social and cultural change.

I balk at agreeing with Kevin Myers's hyperbolic view that history will rank Byrne alongside, maybe even above, Eamon de Valera, though I see the irony. Byrne has helped to dismantle the society envisaged by Dev, he has challenged its taboos and, as a professed Catholic conservative, has been able to do so without the kind of hostility which would have probably scuppered an atheistic liberal.

By blurring the demarcation line between light entertainment and serious current affairs, he has managed to deal with issues in a unique way, winning devoted support from viewers and thus disarming, or at least, disabling his critics.

The show's loose format has been intrinsic to its success: music from some of the nation's best performers, chats with people in the audience, a celebrity guest, perhaps a politician, all interspersed with surprise freebie giveaways, trivial competitions and the odd phone call to remind us that this is happening now. It is live television. The best moments are when "ordinary" people are given the chance to tell their extraordinary stories, sometimes heart-breaking, usually revelatory, allowing viewers to drop through "the trapdoor to the hidden Ireland" as one appreciative journalist memorably termed it.

The package has proven at once both naive and sophisticated, an artful piece of chemistry with Byrne at its core, a pixie figure, rarely fazed, unashamedly schmaltzy, a consummate performer, supremely confident, playing simultaneously to the audience and to the TV cameras, a feat few presenters anywhere in the world have managed to accomplish so brilliantly.

He has been the ring-master of a 37-year weekly circus with the whole of Ireland as his big top, making his guests jump through hoops for the entertainment, and enlightenment, of his audience. Most importantly, to achieve these kinds of debates, Byrne has proved a staunch defender of freedom of speech, withstanding any number of attempts from the censoring forces of darkness. Remember the student who called the Bishop of Galway a moron? He invited the lad back the following week to reiterate his criticism.

Then there were the occasions he gave a platform to previously unheard-of creatures called lesbians and feminists. RTE was picketed but Byrne stood his ground. Some be grudgers have argued that he didn't do so out of principle but only because he knew the value of controversy: it attracted an audience. Maybe, maybe, but the motive is less important than the effect. Television, especially comfortable, popular TV as personified by Byrne's Late Late Show, has a powerful legitimising influence.

By his raising of such matters as homosexuality, divorce and single motherhood and allowing criticism of the Catholic church hierarchy and of self-serving Dail politicians, Irish people were confronted with "alien" opinions and minority tastes while being given a chance to place them in context.

Before I am accused of adopting a condescending tone for seeming to suggest that the "backward Irish" were in need of such tuition, it is clear from the continuing intolerance of British society that it might have benefited from a similar TV show.

Fierce media competition prevented the BBC from performing that kind of public service by generating such a programme. The other problem is the size of Britain's population and its fragmentation.

One of the strengths of Irish society is its relative homogeneity, a reason why a single programme can exert a hold, so the question to be asked as Byrne prepares for his last show next Friday is whether he has served his purpose. Does modern Ireland need him or The Late Late Show any longer? It is tempting to suggest that it doesn't. After all, newspapers have been writing Byrne off through out the decade, but I'm not so sure. People will miss him dreadfully when he has gone, whether the programme survives him or not.

A couple of months ago I watched spellbound as the braggadocio European Commissioner Padraig Flynn, relaxed by Gaybo's easygoing style, made a complete fool of himself. The interview made the headlines the following week.

In spite of Fintan O'Toole's dissection of the sad Sinead O'Connor episode a fortnight ago, I think it should be seen as a mistake, rather than the sign of voyeuristic trend. I recall loathing the way Byrne treated Annie Murphy, but I realised that good, generally, has prevailed. That interview, though, which was surely distorted by Byrne's enduring allegiance to his religion, convinces me of the paradox that is his legacy. In Ireland, as elsewhere, the holy church has been replaced by the unholy media.

That's one for everybody in the audience to think about.