It may have gone somewhat unnoticed, but the Taoiseach has taken quite a few "risks for peace" over the past couple of days. Much has been made, and deservedly so, of Mr Blair's role in driving the search for Monday's agreement on an agenda for the Stormont talks. We know that, upon taking office, the British Prime Minister was surprised (some reports said dismayed) at the amount of his time demanded by Northern Ireland.

But seasoned commentators have surely been equally surprised at the spectacle of Mr Blair, on an official visit to Japan, spending every free moment locked in telephone conference with the North's leading lights, haggling over the detail of the putative framework for a new era in Anglo-Irish relations.

During the recent plenary of the Anglo-Irish Inter-parliamentary Body in London, Irish journalists were invited to No 10 for a fairly lengthy on-the-record session with the Prime Minister. By various subsequent accounts a number of the colleagues went home disappointed and unimpressed. There was nothing in it. Certainly there was no story. Mr Blair had been at his most bland.

To some of us, on the other hand, this was simple confirmation that the Prime Minister knew his way around the minefields. Attempts to lure him into indiscretion were knowingly laughed off: his obvious determination was not to grant a headline confirmation, as Irish sources had maintained, that he was in fact fully "engaged".

After Monday's developments, Mr David Trimble has fewer grounds for questioning the Taoiseach's engagement, or his conviction that an understanding between the Ulster Unionists and the Government is central to any settlement likely to last.

Mr Ahern spoke to Mr Trimble three times last week, twice from Spain, and soon after his return from holiday, and that before the weekend's amazing outbreak of shuttle diplomacy.

By late on Sunday night the UUP leader knew the Taoiseach was in difficulty. Sinn Fein was resisting key elements in the emerging London/Dublin text, the specific acceptance that there would be a Northern Ireland assembly, and the removal of the magic word "executive" to describe the nature and function of the proposed North-South councils and agencies.

By that point, the Ulster Unionist leader knew he had already had removed from the Irish draft a fairly comprehensive list of the subjects which new North-South arrangements might cover, and a quite specific list also of measures aimed at establishing and consolidating a normal peaceful society, including British commitments to dismantle special security installations, reduce troop levels and examine "the pattern and extent of legally held firearms".

On the core issue Mr Trimble refused to yield, leaving the Taoiseach, at it were, to bite the bullet.

The long days of negotiation had taken their toll. There were signs of tension and doubt in the Irish camp. The Joint Framework Document, after all, was an agreed British-Irish text. Why should the pressure be on them to depart from it, at least in terms of language, especially when the potential consequences for the IRA ceasefire were so difficult to calculate?

In the end, with a nod and a wink from the Ulster Unionist and SDLP leaderships, the Taoiseach took the gamble; traded "executive" powers for "suitable implementation bodies and mechanisms for policies agreed by the North-South Council"; and prayed Sinn Fein would stay in the talks.

It was a considerable risk, underlined by Mr Trimble's assertion that the final product represented "80 per cent" of what he wanted. By any objective analysis it would seem to fall well short of that. But yesterday's headline, "New push for peace delights unionists", only served to illustrate the precarious nature of the Stormont roller-coaster.

And there's the rub. It is a rollercoaster, promising and inevitably delivering highs and lows. And Mr Trimble surely knows that in as much as he has received he will be expected also to give.

THE UUP leader may affect to believe that his current reasonably cheery disposition owes all to his "understanding" with Mr Blair. He will also surely recognise that it owes something to a marked change in the attitude and approach of the Irish Government, for which Mr Ahern, encouraged by key players in the Irish diplomatic mission, is responsible.

In past times Dublin has appeared as a matter of course to reject the unionist agenda out of hand on the simple maxim that "if it's good for them it must, by definition, be bad for us". This instinct led to the absurdity, for example, of strenuous resistance to the unionist argument for the creation of a Select Committee on Northern Ireland Affairs at Westminster (as it had done, years before, to the grant of increased parliamentary representation following the fall of Stormont).

No matter that the "democratic deficit" demanded Westminster reforms, or that, despite the expectations of unionist integrationists, such reforms would not materially change the Northern political landscape. The very fact that these were unionist demands saw them invested with huge symbolic significance which inevitably carried connotations of victory and defeat.

Similarly, for years, Dublin has been dismissive about unionist arguments over the territorial claim, and their proposals for a wider agreement spanning "the totality of relationships" within these islands.

The Taoiseach appears to have sensibly calculated that an engagement with unionists on their own terms is the necessary prerequisite to their engagement on the wider agenda necessary for a "balanced" constitutional settlement.

The offer of that engagement was spelt out on Monday. The text carries undoubted challenges to nationalists on the vexed question of security. But it comes complete with a challenge to unionists to embrace that wider agenda, with its still-to-be-defined detail on justice and equality, parity of esteem and aspiration, and "meaningful" North-South co-operation and harmonisation, without which there is little realistic prospect that Northern nationalists will be reconciled to the reality of the Union.

However, Mr Trimble's biggest challenge of all, ironically, may be to make something "meaningful" of the now general commitment to a new Northern Ireland assembly.

Some nationalists, and doubtless most republicans, will incline to see the emergent assembly as a straightforward victory for the Ulster Unionist leader. And unionist rhetoric certainly encourages the notion that it is a central ingredient of their declared bid to unravel the 1985 Anglo-Irish Agreement.

London and Dublin have always accepted that devolution could have profound implications for the 1985 accord. But that, and the consequences for the standing machinery of the relationship between the two sovereign governments, all depends on the scale of power devolved.

And here's the irony. At Stormont Sinn Fein has been promoting the idea of a series of regional councils. In the context of Mr Blair's constitutional reform in Britain, Mr Trimble appears to prefer an assembly more akin to what is emerging for Cardiff than for Edinburgh.

In other words, the unionist preference for limited devolution on the regional council model has survived the transition from Molyneaux to Trimble. The SDLP, by contrast, for all nationalism's historical aversion to devolution, wants to maximise the powers of the new Northern Ireland institutions.

Mr Trimble might want to engage them on that front. If he doesn't, while the assembly may prove a useful adjunct to the Anglo-Irish Agreement, it will carry no conviction as a replacement for it.