As the road approaches the Shell gas terminal at Ballinaboy on Ireland's Atlantic west coast, only the posters pinned to the telegraph poles give any hint of the country's longest-running environmental protest.

The uninterrupted view of green fields running down to the ocean could be a screen-grab from an advertisement for the Irish Tourist Board.

But for the past four years this remote but beautiful corner of north Mayo has been the setting for a bitter industrial dispute. At times, hundreds of police have been deployed to break up pickets. And this summer, the tiny hamlets of Glengad and Rossport looked on as two Irish navy frigates moored in Broadhaven Bay, apparently there to stop the protesters' dinghies interfering with the Solitaire, Shell's vast pipe-laying ship.

Exactly how a grass-roots campaign led by a retired schoolteacher and a handful of hill farmers and lobster pot fishermen has frustrated Ireland's most important energy project perplexes industry experts.