Donald Macintyre: Will tomorrow's statement save the peace process?

'In the best-case scenario, the IRA will make a move on decommissioning to coincide with Blair's package'

On the continuous roller coaster that is the Northern Ireland peace process, the parties are once again nearing the end of that slow, ominously relaxed crawl up the gentle incline before the cars hurtle sickeningly and inevitably downwards at breakneck speed.

After a period of what has seemed like deceptive calm in negotiations, events may this weekend move very fast indeed. Probably tomorrow, the Irish and British Prime Ministers intend to introduce their – theoretically at least – "non-negotiable" package of measures designed to keep the devolved institutions in being, save the Good Friday Agreement, persuade the IRA to begin decommissioning their arms, and, ideally, restore David Trimble as First Minister when the assembly reconvenes in September.

In Northern Ireland, fortunes can and often do change in an hour, let alone a day. But at the moment the omens could be a lot better than they are. The mood in the moderate unionist circles that Mr Trimble represents was fairly bleak yesterday, made all the bleaker by a series of leaked concessions to republicans contained in draft versions of the package. Some of them, especially on policing, would be hard for Unionists to live with even if accompanied, or swiftly followed by, some substantive step by the IRA on decommissioning – which it was last night far from certain that they would be. Put bluntly, the deep fear among Unionists was that they would be paying an intolerably high price for a product that may not even be delivered.

There have been several changes in the weather since Messrs Blair and Ahern took the parties off to Weston Park on the Staffordshire-Shropshire border in an effort to find a way through the decommissioning impasse which had led to Mr Trimble's resignation in the first place. At first it seemed to almost all of them, including the two governments, to be pretty hopeless. When they came away there was a mood of cautious optimism that the IRA might at long last be prepared to make a start on putting their arms beyond use.

Mr Trimble, for example, was initially disinclined to take the talks very seriously because he had noted the absence of two senior figures on the IRA Army Council who are invariably present when any advance is expected from the Provisionals. When he mentioned this to Bertie Ahern, the Irish Taoiseach, however, Mr Trimble was pleasantly surprised to be told that they were indeed keeping a discreet presence in a hotel across the lake.

But there was a little more to it than that – a sense among the two governments that the IRA would not finally allow the devolved institutions, and their two ministerial posts in the Northern Ireland government – to founder by once again refusing a further step on decommissioning. They were under huge pressure from the Dublin Government, from the press in Ireland, and from Irish America to begin disarming. If they refused, their obduracy would inevitably be blamed for the crisis. Or so, at least, it seemed.

By yesterday some of this optimism had begun to evaporate. It could return again as early as today. But the question haunting Unionists yesterday was whether these assumptions underestimated the renowned negotiating skills of the republicans, and, at least in Unionist eyes, the susceptibility to them of the Dublin and London governments.

As ever, the principal issues at the heart of the Weston Park talks were the demands of the republicans. They want complete fulfilment of the Patten report on policing and more besides – for instance, a ban on the use of plastic bullets; a further reduction in the British military presence, particularly in South Armagh; and further amnesties for paramilitaries "on the run". The two Prime Ministers are seeking to address these issues in their package in the hope that it will persuade the IRA to start decommissioning.

In the best-case scenario, the IRA would make a carefully choreographed, prompt and dramatic move on decommissioning to coincide with the Blair-Ahern package. The further changes on policing reform, ranging from recruitment of senior level Irish gardai to Northern Ireland's police service, to the inclusion, at some point, of ex-paramilitaries on local police boards, would be hugely painful for Unionists – perhaps even too painful for them to accept. But at least there would be a prize in sight.

In the worst-case scenario, from a moderate Unionist point of view, the IRA would respond to the Blair-Ahern package by saying merely that the proposals would need to be considered. The Unionists would be driven by the internal force of its own hawks to reject the proposals immediately. And the republicans would then seek to shift all the blame for the impasse to Unionism .

In between, of course, there several shades of grey; several unanswered questions. Would the inclusion of ex-paramilitaries on the police boards, if it happens, be immediate and therefore require a change in primary legislation, – or would it be merely a statement of future intent? (The first would be especially explosive for rank and file Unionists who fear that Northern Ireland policing will be downgraded.) Would any decommissioning – always assuming there is any – be merely the sealing of the dumps already open to inspection (which the Unionists believe have already been compromised, thus negating much of the force of such a gesture)? And if there is a breakdown, would the government seek to buy time by a one-day suspension of the assembly – or, surely less likely, dare to hold fresh assembly elections which would result in increased votes for Sinn Fein and the Democratic Unionist Party at the expense of the moderate centre and perhaps of the Agreement itself?

The Ulster Unionists are critical of the British Government. They believe the tactic of forcing another deadline was too risky. They also believe that the Government – having first released paramilitary prisoners, without any action on decommissioning in return – has come perilously close to playing some of its last cards with the republicans. Nor is the fragility of their position improved by the Government's intention to exclude the DUP from pre-briefings on the Blair-Ahern package – thus paradoxically strengthening its moral position. Even if there is a convincing IRA gesture, they may find the price unacceptable – in which case they will indeed take some of the blame.

But the game is not quite over. The final Blair-Ahern text has not been completed. It is surely inconceivable that it will contain the most neuralgic and inflammatory elements for the unionists if there is no prize from republicanism in return.

It is by no means clear that if the IRA do not respond, the blame will so easily be shifted to the Unionists. The Presidential election means that Sinn Fein has fewer friends in Washington than it had. Forty-eight hours before the anticipated Blair-Ahern agreement, the heat is still on the IRA.Will it produce the results that Dublin and London are hoping for?

d.macintyre@independent.co.uk