The next four months will probably determine politics here for the next 10 years. The next month really is that pivotal. Not only will it determine whether Ireland can keep the IMF from the door – which right now looks a 50-50 call – but it could go a long way towards determining which of the opposition parties will lead the new government.

We already have a decent idea of what is in store. By the middle of November, a four-year plan will be sent by the government to Brussels for approval. The plan will lay out, in significant detail, the spending cuts and tax increases that will be introduced to bring Ireland's budget deficit down to 3% of GDP by 2014.

The savings required to reach that target are likely to be the region of €12bn-€13bn. But there is no 'Plan B'. "The markets are in no mood for saying 'take another year or two to get there'. They want to see a detailed plan. You can't be bluffing. They want to see the gory details," was the verdict of one economic expert last week.

What isn't clear, though, is if there will be an opposition support for those gory details.

Whether through clever planning or sheer luck, the Green Party has achieved what it set out to do 10 days ago in getting the four main parties into talks about reaching a consensus on the budgetary plan.

Only they can know the real motivation for opting to do a solo run on the issue. Was it done on the hoof to divert attention from John Gormley's comments about a national government or did the Greens go it alone because they feared that Fianna Fáil would either knock the proposal on the head or even try to appropriate it?

Equally only Brian Cowen can know why he took the approach he did over the past week or so. He has a point when he says that he never ruled out the idea of consensus but neither did he enthusiastically embrace it. Until, that is, he wrote to the leaders of the two main opposition parties.

Looking in from the outside, it would appear the Taoiseach took the hump at the Greens announcing the proposal without running it by him first, before coming around to the view that it had brought about a desired outcome. After all, it was Cowen who had first suggested some form of opposition input the previous weekend.

However it happened, the Greens are feeling chuffed with themselves this weekend. And clearly there are merits in the consensus approach for the government. Economically, it is hugely important that the financial markets are convinced that the next government – certain to be made up of Fine Gael and Labour – is willing to do what needs to be done. Politically, it turns attention on the opposition parties and forces them to come up with credible plans to tackle the budget deficit.

And how Fine Gael and Labour respond to that challenge could go a long way towards deciding the next general election.

It is already obvious that Labour will not touch the consensus proposal with a barge pole. Eamon Gilmore's Evening Herald interview, when he on the one hand committed his party to getting the deficit down to 3% by 2014 and on the other ruled out pretty much every one of the measures that will be needed to get there, spoke volumes in that regard. As did his incredibly cool response to Cowen's invitation.

Labour will go through the motions of getting involved – it can't be seen to do otherwise – but it will be looking for the first credible opportunity to exit.

Fine Gael figures are a lot more enthusiastic – some of them anyway.

"There is a division in Fine Gael on how to approach this, between the older members and the younger TDs," one deputy admitted. The attitude of the older generation was summed up by a senior figure last week: "F**k them. Let the government bring in its own budget".

But the other view – which seems to be in the majority – sees this as an opportunity to "put clear blue water" between Fine Gael and a Labour Party that they feel has been getting far too easy a ride in recent months.

One frontbench figure told the Sunday Tribune: "The government see the four-year plan and the proposal for consensus as an opportunity to flush out the opposition. But we're quite prepared to be flushed out. We see the four-year plan as the chance to flush out Labour".

Fine Gael certainly won't give the government a blank cheque and support its specific measures to bring the deficit down. There won't be a joint government and Fine Gael four-year plan – far from it. But Fine Gael will endorse the total figure required in savings and may sign up for the year-on-year figures, including the likely €4.5bn-plus required for 2011.

Party figures are also confident that its own plan for finding the savings – which will be more concentrated on cut-backs than raising taxes – will differentiate it from the government's approach and be a lot more credible than what Labour is proposing. "It's easy to come up with €2-3bn in alternative cuts and taxes but you can't just tax the rich and close quangos and get to the €12bn required," one senior TD said.

It remains to be seen whether or not the increased focus on the credibility gap in Labour's budgetary plans will make any difference to the electorate. Many politicians on both sides of the house are unconvinced that voters will thank any party for giving them bad news. But most in Fine Gael believe the party has little choice but to take this stance. It "can't compete with Gilmore on personality" and it is what the party's potential support base expects.

The two main opposition parties will be briefed by the Department of Finance on the budgetary situation tomorrow and there is a strong likelihood of talks with Fianna Fáil and the Greens later in the week to see if common ground can be established.

However the talks go, there is little prospect of a new era of cooperation between the main political parties in the national interest. But some level of agreement on the broad parameters might be on. At the very least it has focused attention on the genuine crisis facing the Irish state. By this time next month the future – both economically and politically – will be a lot clearer.