There could be no going back. Not for unionists. Not for nationalists. The days of triumphalism, of supremacy and exclusive tribalism were fading. The Belfast Agreement and the will of the sovereign people would prevail.

Tony Blair spoke of change and growth, of co-operation and friendship, of common interests and of peace. His speech to the joint Houses of the Oireachtas wasn't contentious or impasse-shattering. But the presence of a British prime minister, after nearly 80 years of independence, spoke volumes about the thaw in relationships between the two governments.

It was a delicately poised speech: designed to entice and reassure, without being patronising; to advocate and challenge, without being threatening. The Belfast Agreement was based on three, not two, sets of relationships. And while people on this island might concentrate on internal structures, Mr Blair held the relationship between Ireland and Britain to be the key determinant.

The core of his political approach was, he said, very simple. In Northern Ireland, unionists wished to belong to the UK; nationalists to Ireland. But there were no absolutes. And people there could "live together more easily if we, Britain and the Irish Republic, can live closer together too."

In that context, Bertie Ahern's reference to the possibility of Ireland rejoining the Commonwealth was a straw in the wind. Not that it would happen overnight. But the Taoiseach favoured a debate on the subject, following representations from a variety of interests. And Mr Ahern would "not argue against rejoining". It was as far as a cute politician, who was also leader of Fianna Fail, could be expected to go.

Membership of the Commonwealth would be no big deal. It is now a voluntary club of 54 countries - many of them republics - that provides a network for academic, political and economic exchanges. Ireland left the Commonwealth in 1949, when the first inter-party government declared a Republic. Since then, global power structures have been transformed. And Britain is only now emerging from what Mr Blair described as "its post-empire malaise".

IT MAY be a bigger window on the world than the EU, but its importance is more imaginary than real. If Irish membership would salve unionist fears - and a senior unionist has already described it as a very, very important and historic development - then club membership may be no bad thing. But we should keep matters in perspective.

Under the Belfast Agreement, a British/Irish Council will reflect and explore the opportunities for co-operation between these islands in areas such as transport, education and the fight against illegal drugs. And linkages will be established between the parliaments and assemblies in Northern Ireland, Wales and Scotland, as well as Britain and Ireland.

These developments are designed to strengthen the position of David Trimble and reassure unionists that they will not be abandoned or betrayed. But there is a larger picture. And Mr Blair kept his eye firmly fixed on it when he spoke about a new British/Irish relationship in Europe that would be informed by friendship and common interests.

Pragmatism has always ruled in British politics. Mr Blair sees a resurgent Britain and a changed Republic forging new bonds in order to gain a stronger voice in Europe and "to shape its future in a way which suits all our people".

A common approach, he said, could make a political difference in Europe in areas such as economic co-ordination, foreign and security policy, the environment, crime and drugs. The two countries had to make the single currency a success and reform the international financial system. They also had to retain decision-making on issues such as tax, education, health and welfare.

It was all about common interests and objectives. Putting aside old hates would not be easy. But there was so much to celebrate in terms of shared culture. And to pursue in terms of common prosperity.

The programmes of national renewal that were now under way in both Britain and Ireland would be strengthened, Mr Blair said, by a co-ordinated approach within Europe.

The Prime Minister's own background - his Irish mother from Donegal and his regular childhood holidays in that county - was unveiled as evidence of his good faith. But his "entree" to the Oireachtas had been secured long before, particularly in his contribution to the Belfast Agreement.

No attempt was made to disguise the difficulties besieging that agreement, in terms of forming the Northern executive and decommissioning arms. But Mr Blair was still optimistic. They had come too far to go back.

The two governments were implementing their portions of the agreement, through prisoner releases, a review of policing, scaled down security and changing Articles 2 and 3. It was now time for the Northern parties to do likewise by establishing new North/South bodies, setting up new institutions and taking the gun out of politics for ever. But nothing is that simple in Ireland. The "integrity of the ancient quarrel" and the dreary steeples of Fermanagh - alluded to by Winston Churchill - endure. Progress is made in inches. Great leaps forward occur elsewhere.

In that regard, the Government hopes agreement will be reached on the North/South implementation bodies early next week. The number and functions of Northern ministries may also be decided. The way would then be open to legislate for these bodies in advance of the scheduled February transfer of powers.

David Andrews hopes that when all these institutions have been legislated for and are ready to go, the IRA may find the flexibility to decommission weapons. The issue between Sinn Fein and the Ulster Unionist Party was, according to Mr Andrews, "essentially one of trust". What was needed was a fresh approach to give confidence to both sides to move forward.

Mr Blair offered the Northern parties a double-edged solution: support for both communities and their aspirations within a framework built on consent, agreement and peace, as in the Belfast Agreement; or an increasing irrelevancy as the two governments moved forward into a new and productive arrangement in which the "ancient quarrel" had no place.