The political weather forecast for today is stormy. Not just sleet and rain but metaphorical rocks and boulders will be flying. There will be gale-force winds and a very large quantity of hot air, especially in the vicinity of microphones and TV cameras.

Media madness is likely to be the order of the day. Reporters and camera crews will be at the pins of their collars to cover all the angles.

This is a critical day in the life of the peace process. And if it is handled wrongly the talks, and ultimately Northern Ireland itself, could go hurtling into the abyss.

Sinn Fein, as so often, is the focus of attention. And as so often in the past, its associates on the paramilitary side have queered the pitch for the political leadership.

Apart from the Ulster Unionists, one detects no great appetite among the talks participants to exclude Sinn Fein, but last night sources said there seemed no other option.

Any exclusion is likely to be short. There are unconfirmed reports that it may last only three weeks and be over by March 10th. During that time, sources suggest, Sinn Fein would continue to have access to all the facilities of the talks apart from plenary sessions and committee meetings. Even ministerial meetings would not be ruled out.

The precedent was cited of the Ulster Democratic Party, which is on the verge of readmission, having departed on January 26th. Last week it held a meeting via video-link to London with the North's Political Development Minister, Mr Paul Murphy.

There is considerable sympathy for the political leaders of the republican movement. Sceptical unionists apart, it is accepted by many participants at government and party level that Mr Gerry Adams is sincere in his commitment to the political process.

But the Mitchell Principles must be maintained. Talks insiders take the view that the principles have been breached and that Sinn Fein, whatever its protestations, will have to pay some price for this.

At the same time, there is a recognition that the breach may well have been as much a deliberate attempt to sabotage the political efforts of Sinn Fein leaders as an expression of impatience and frustration with the slaughter of innocent Catholics over recent months.

Temporary retirement would thus appear to be the fate of Sinn Fein at Dublin Castle today. The republican party will fight like tigers on the issue, and there will be fierce denunciations of the alleged unionist plot against the peace process.

The unionists on the other hand will have to suppress any chortles of triumph and be on their best and most statesmanlike behaviour if they are to make the most of the republican movement's own-goal.

Behind the headlines and away from the microphones and cameras, talks insiders say there have been fairly significant strides along the road to an eventual agreement.

"Everybody has achieved a huge amount by being there, and it's been a really good game so far," was how an informed source put it.

Over the weekend, politicians and mandarins alike have been exploring all possible avenues by which the anger of the unionists could be assuaged without pushing the republicans back to full-scale war. Suggestions that the IRA ceasefire will break down if Sinn Fein is excluded from talks plenaries were described by republican sources as "over the top".

The Grand Plan, talks insiders said, was that Sinn Fein would be "everywhere except at the table" for the next few weeks. The party would be kept out of the parlour but free to roam the rest of the house: it would have continued use of talks facilities and be kept informed of developments in the process.

"There is no question of excluding them from the process," a senior source said. "There are many ways they can feel they are being included though not at the table."

It is understood the White House is fully backing the "yellow card" approach to Sinn Fein but, like others, has not given up examining all the options.

If indeed the republicans are readmitted by March 10th, Mr Adams and Mr Martin McGuinness would probably still be able to rub shoulders with Mr David Trimble and the other party leaders at the White House on St Patrick's Day. But in the current climate, handshakes on the White House lawn seem like a wild fantasy.

Threats of legal action by Sinn Fein were taken with varying degrees of seriousness by other talks participants. "That's a load of tripe," said one official. "Anything to do with the law is a real worry," cautioned another.

One long-distance peace processor lamented that today's events were "like a Greek tragedy. You can see the end coming but you can't do anything about it."

Well-placed sources said Sinn Fein hadn't a snowball's chance in hell of staying at the talks table, especially given the "rock-solid" view in London that the party must be penalised over recent events.

For its part, Sinn Fein has to take account of anger in republican areas, especially west Belfast, over the wave of sectarian killings of Catholics and the jaundiced view in that community of the RUC's efforts to apprehend loyalist assassins. This anger will be given full expression by Sinn Fein representatives today and throughout the week.

Official sources in Dublin said last night they expected the complaint against Sinn Fein to be lodged by the British government, "because they have the evidence". The parties, including Sinn Fein, would be given an opportunity to comment.

The proceedings would then be interrupted, and there would probably be bilateral contacts. "The two governments will go away and make a decision, hopefully in the afternoon."

There is anxiety that the talks should not be deflected any longer than necessary from the proper business of the week, which is discussion of the all-important Strand Two relationship between North and South. In a sense, the Sinn Fein imbroglio has come as a godsend to the unionists, who had no intention of being seen by their followers making an enthusiastic contribution to the Strand Two debate in the Irish capital.

Among the many pressures on the two governments is the likely reaction from the unionists if disciplinary action is not taken against Sinn Fein.

There have been hints from unionists about "tactical withdrawal" and "considering our position".

Republicans are angered by what they see as excessive political sensitivity to the feelings of the UUP. Republican sources said neither the two governments nor the White House wants Sinn Fein excluded from the talks: "This is all coming from the unionists, who remained silent during the onslaught on Catholics."

Republicans said they were "considering all the options", and it is clear they are going to put up the political fight of a lifetime to remain at the table. Dublin Castle today is going to be a lot like Donnybrook Fair.