In the wake of his historic meeting with Northern Ireland's Prime Minister, Terence O'Neill, in January 1965, Sean Lemass clearly had to mollify Eddie McAteer, the leader of the Nationalist Party in Northern Ireland. McAteer had not been consulted prior to the visit and was promptly invited to Dublin. On January 21st Lemass wrote to Frank Aiken informing him that McAteer's party was contemplating taking the position of official opposition at Stormont but was "in some difficulties regarding it."
Lemass had suggested that the Nationalist Party needed "a firm and logical basis for effective political action", and to this end should reaffirm their commitment to Irish unity, "recognising that this might be achieved on a federal basis".
With the adoption of such a policy, he believed, there was "no reason in principle" why McAteer's party should not work to improve the government and the laws in Northern Ireland, with the goal of "equality for all citizens and effective practical co-operation between the two areas."
Aiken, invited to comment, gave broad approval to the line taken by Lemass, but warned against the use of the term "federal" to characterise the offer to Stormont that its powers be devolved from Dublin rather than London.
"Federal constitutions the world over would, no doubt, be examined in search of precedents of all sorts. We might well be faced with a demand for three parliaments and for equal representation of the Six Counties and the 26 Counties in the all Ireland parliament.
"An all Ireland Constitution of this kind with a built-in veto would render normal government impossible - as happened in the recent tragic case of Cyprus."
McAteer was to remain uncomfortable with what amounted to the new agenda - and it could be said the new axis - in NorthSouth relations, as ministerial summits and pragmatic co-operation between officials became routine in the aftermath of the Lemass-O'Neill breakthrough.
The joint marketing of Ireland as a tourist destination was soon on the agenda. But even such an initiative - with obvious benefits on both sides of the Border - was fraught with difficulties.
Should the map of Ireland show the Border? Should different colours be shown for North and South? If so, which colours? Should it be Derry or Londonderry? In what context and how often should the word "Ireland" be used?
These were among the questions which vexed the officials and politicians.
After many months' work, progress was thought to have been made. But when a promotional leaflet for the American market, "Ireland and Britain: two historic islands to tempt you across the Atlantic," was forwarded to Iveagh House, there was consternation. The accompanying map seemed proof of Murphy's Law.
Brendan Nolan, First Secretary, complained. "They made a real hash of the map which is now headed `Ireland and Great Britain' and our Border is marked and referred to as `the customs boundary between the UK of GB and NI and the rest of the country which is an independent sovereign state'!!!"
Nolan's three exclamation marks show that he thought this wording daft when he encountered it on a map of Britain and Ireland. What he did not recognise was that it was a direct quotation from one of his colleagues in Iveagh House!
The wording is unhappily ambiguous: it suggests quite different information depending on whether it accompanies a map of Ireland, or a map of Ireland and Britain.
That it originated from within Iveagh House is shown by the use of just these words in a briefing note for Mr Lynch from the Department Secretary, Mr Hugh McCann, before Mr Lynch met Capt O'Neill in December 1967.
But this was not Mr Nolan's only complaint about the map: "`Northern Ireland' encroaches in Donegal!! The `Mountains of Mourne' are everywhere except in their proper place."
Moreover, in the "exhausting correspondence", it had been agreed that the map would show only Ireland and that there would be no footnotes. "Because of the nonsense made by the inclusion of Britain we shall have to reopen the can of worms again."
Such setbacks were inevitable. But by the Lynch-O'Neill summit of December 1967 what may be called the Lemass-Whitaker policy had borne considerable fruit.
This is manifest from the extensive - if often mundane - files entitled, "Social, Economic and Cultural Co-operation between Twenty-six and Six Counties" which detail the efforts of many Government Departments to respond to Dr Whitaker's call for an audit of North-South co-operation.
Further evidence of progress can be gleaned from a letter which Erskine Childers sent to the Taoiseach in April 1967.
He was reporting on a meeting in Bonn with the Northern Ireland Prime Minister, Terence O'Neill. They had met by accident and had spent over three hours together.
"He was in great form and recounted anecdotes, Paisley stories and occasions when he was treated as coming from the South at receptions etc." He was enthusiastic about the new policy.
O'Neill said that "Paisley had created an undercurrent of suspicion, which would disappear in time" provided no "inflammatory speeches" were made from Dublin and "if his own colleagues refused to be intimidated by Paisleyism."
Childers believed that O'Neill was "in advance of his Cabinet in thinking and obviously loathes intolerance even if he has to temporise officially." Childers reported O'Neill's belief that Unionism "could not survive in a fog of prejudice and bigotry."
But Eddie McAteer remained discomfited. By November 1967 he was complaining about a liberal speech made by Sean Lemass - a year after he had ceased being Taoiseach - to the New Ireland Society at Queen's University Belfast.
McAteer confided that he would "be greatly disturbed" if the members of the Lynch government shared Lemass's line. He complained: "The Nationalists feel that they are now nobody's children."
But their grievances did not go unrecorded in the Department of External Affairs. Indeed the newly-released files show how Northern Ireland was at a crossroads in 1967: along with the optimistic scenario envisaged by Childers and O'Neill, there were serious rumblings of nationalist discontent.
Another indication of change could be gleaned from Paul Keating's report from the Irish Embassy in London in which he admitted the demise of the old guard anti-partitionists: the United Ireland Association was "now doing little more than ticking over."
It was "somewhat at a loss" to understand the talks with O'Neill and the initiative was passing to Clann Eireann, "the British wing of Sinn Fein", and to the Campaign for Democracy in Ulster, which was "growing fast."
The more pessimistic analysis of some of these emerging pressure groups is also chronicled in the files: the Campaign for Democracy in Ulster, the British Society of Labour Lawyers and the Campaign for Social Justice in Northern Ireland.
And Iveagh House noted the verdict - "totally depressing" - of the Lancaster Peace Research Centre: "The segregation imposed on the Catholics amounts to a system of apartheid."
Such issues were not on the agenda in the North-South talks. McCann in his briefing note for Lynch prior to the December 11th summit with O'Neill, ChichesterClark and Faulkner specifically listed the areas of discrimination, adding that these issues were "emotionally charged" and were consequently "outside the scope" of the talks.
As they sat around the cabinet table in Stormont, these protagonists could not have known that the three unionist politicians were shortly to become the last three prime ministers of Northern Ireland.
Their agenda on that December day in 1967 eschewed the very issues which were to cause their downfall - and it was little different on O'Neill's reciprocal visit to Dublin a month later.
Instead they discussed cross-Border trade, the threat of foot and mouth disease and possible loans between the National and Ulster Museums. Satisfactory co-operation was reported in the fields of tourism and electricity supply.
Whitaker also notes a "brief reference" from Lynch to "the difficulty of maintaining two symphony orchestras without one bidding against the other for instrumentalists."