Behind every great headline there's at least one good story. Which, if it's strong enough, is bound to be followed by a demand for an inquiry. At best the inquiry is into the substance of the report; at worst it's about how, why and in whose interest it came to light.

The Sunday Independent's front-page news on September 5th, 1948 qualified on all counts. The headline "External Relations Act To Go" was as dramatic as the climate of the time and the style of the paper would allow.

The report was well-founded. The first Fine Gael-led coalition - five parties and six Independents - was indeed about to break the remaining links with the British Commonwealth and declare a republic.

The repercussions echoed around the world. (The only Irish news to have won such international attention for years had been Eamon de Valera's visit to the German legation to offer condolences on Hitler's death.)

And the source? The dispute as to whether this was a cleverly timed leak or a case of old-fashioned journalistic intuition has only lately been resolved. When the report appeared, the Taoiseach, John A. Costello, was visiting Canada and when asked about it was unsure.

Leaving the Commonwealth had been discussed by the cabinet, though whether formally or with a clear result is still debated. But was this the time or the place for an announcement? Costello eventually decided that it would be wrong to deny the report, but not before he'd indulged in some soul-searching about its impact and speculation about its source.

Both figure in two recent books: Eithne MacDermott's Clann na Poblachta, a colourful account of the party, and David McCullagh's A Makeshift Majority, the meticulous story of the coalition.

Costello's Canadian tour, his first as Taoiseach, had not been going well before news of the report was sprung on him. Now it attracted serious attention at home and abroad. But once the question was raised, so were the Taoiseach's suspicions.

As Ms MacDermott reports, he felt that "an article penned with such `apparent authority' could not have been written on the basis of `intelligent anticipation' ", as the paper's editor, Hector Legge, claimed.

Suspicion fell on two members of the cabinet, the eloquent, outspoken and conservative James Dillon, and the chief advocate of a break with the Commonwealth, Sean MacBride of Clann na Poblachta.

Both were friendly with Legge and had reasons for making sure the proposal was aired. Costello acknowledged the consequences in a letter to Bill Norton of Labour, which David McCullagh quotes:

"As you well know, I very nearly, if not actually, `declared' the Republic - in Ottawa above all places. I will explain when I return why I decided to state publicly that we intended to repeal the External Relations Act.

"It was really the article in the Sunday Independent that decided me, although I had intended to tell Mr Mackenzie-King [the Canadian Prime Minister] . .of our intentions in this regard."

Even in a letter to a cabinet colleague, this was an impressively straightforward admission about the making of a major decision - an example few of Costello's successors followed.

As to who spilled the beans, after 50 years, MacBride's secretary, Louie O'Brien, has confirmed that he did.

He had obviously grown impatient with the progress being made by the government towards repeal of the External Relations Act, which was his project. So he seized the opportunity presented by Costello's Canadian tour to speed things up.

The Sunday Independent was to all intents and purposes a Fine Gael paper. Its editor was friendly with several well-placed members of the party; suspicion would fall, not only on MacBride, but on other, equally likely sources.

What mattered to MacBride was that the decision was put beyond doubt, which it was, once Costello confirmed it. To make doubly sure, MacBride spoke to Costello on the telephone, encouraging confirmation.

This, in turn, gave Costello an opportunity to assert that he, and not the Minister for External Affairs, oversaw foreign policy.

Whoever devised and presented that policy, no one can deny that it was in tune with the times, as the public welcome for the official declaration showed, in spite of de Valera's reservations.

I remember well listening to my father and his friends discussing these events. There was a sense of unfinished business in the air. Indeed, looking back after 50 years, it still seems that in the late 1940s we were under siege.

Wartime shortages persisted. Country roads like ours had yet to be tarred; even parishes that were within a few miles of Ardnacrusha and the ESB's Shannon scheme had not been supplied with electricity.

A teachers' strike closed most schools in Dublin for months in 1946 and the bitterness generated in the powerfully influential INTO spread to politics.

My father, who had backed de Valera since 1918, railed against Dev's education minister, Tom Derrig, and fell out with the party. His anger turned to support for Clann na Poblachta, which was founded at the height of the strike.

In the years before the 1948 election we'd gathered at the bridge which marked the boundary between Limerick and Clare to welcome Dev as one of our own. Shortly after the election Costello crossed that bridge. Over it hung a banner which announced: "Clare welcomes her son the Taoiseach."