IN politics, everything changes and everything stays the same. This week 16 years ago, a young Michael Lowry – as the key, behind-the-scenes mover and shaker in Fine Gael – was almost single-handedly putting together a government pairing old foes John Bruton and Dick Spring with Democratic Left to form an historic rainbow coalition.

Fast forward to the present day and there is a different historic coalition in place (just about) but, come Tuesday, Lowry will once again be the pivotal character in the political drama that will unfold. His vote will determine whether the budget – arguably the most crucial in the history of the state – will pass or fail. The significance of that result, in terms of Ireland's already battered reputation internationally, cannot be overstated.

There were hopes in recent weeks that one or both of the main opposition parties might abstain, or that a few of their TDs might miss the key votes, to ensure the appalling vista of the budget failing to go through would be avoided. But such hopes have largely evaporated in recent days and, in hindsight, one wonders how realistic they ever were.

The Labour party didn't get where it is this weekend – 24% in the polls compared to its traditional rating in the region of 10% – by endorsing painful budgetary measures. Quite the contrary.

And the feeling in Fine Gael is that its natural tendency over the years to 'do the right thing in the national interest' has been one of the main reasons it has always had to play second fiddle to the cuter, more hard-headed Fianna Fáil.

Senior Fine Gael figures insist there was a mood within the party to "play our part", but they acknowledge that this has disappeared over the past week.

"There's been a hardening of attitudes," one senior TD said last week.

They say this is because of the government's refusal to meet them halfway, particularly over Enda Kenny's suggestion to bring forward the budget to last week and have it all over with by the end of December.

"Fianna Fáil has been trying to string the whole thing out for as long as possible," the TD said.

But the fear of being outflanked by the Labour Party with a general election just a matter of weeks away must also have been a significant factor.

There are clear divisions within Fine Gael as to what is the best strategy to adopt with regard to the budget. But the majority view is that it would be madness to endorse what is certain to be a deeply unpopular budget and allow Labour – and, to a lesser extent, Sinn Féin and other left-wing candidates – a clear run at reflecting the public's hostility to large tax increases and savage spending cuts.

While it is possible that Fine Gael will not vote against any excise duty increases on Tuesday night, the chances of it endorsing or even abstaining on the key social welfare bill appear close to zero.

The same holds for Labour with bells on. Even by its recent standards, Labour has ratcheted up the rhetoric in recent days. Joan Burton's statement, post the announcement of the details of the EU/IMF deal, that the country was banjaxed, raised eyebrows throughout the Dáil, not just in the government benches. And Gilmore's angry, desk-thumping insistence that his party would not be bound by the terms of that deal was closer to Sinn Féin's position than the party's inevitable coalition partner, Fine Gael – fallout from the Donegal South-West by-election result perhaps?

Both main opposition parties launched their pre-budget documents on Friday. However, the real focus of the submissions was not on next Tuesday but on polling day in February or March. Labour was not going to hand a stick for Sinn Féin and other left-wing parties to beat it with by committing to cutting social welfare, even though getting to its €4.5bn target of savings (never mind €6bn) is impossible without that.

Similarly, Fine Gael had its own support base in mind when it backed social welfare cuts but ruled out tax increases and reductions in child benefit. The sums do not add up on either plan, but the politics do.

Despite what they say in public, the two main opposition parties desperately want the budget passed – if it isn't it will be left to them to introduce the €6bn in cuts and tax increases. But they have made a call: the budget will be passed without them and they are not going to be seen to throw a lifebuoy to a drowning Fianna Fáil.

That puts Lowry and Jackie Healy-Rae centre stage. Assuming that all the government deputies, along with the three Fianna Fáil TDs who have lost the party whip, support the budget, the coalition has 80 votes. The best the opposition can muster is also 80 votes. If Lowry and Healy-Rae back the budget, it will go through. If they vote against it, it will fall. If they abstain – the most unlikely outcome – it would probably pass with the casting vote of the ceann comhairle.

Of the two, Lowry is clearly the key figure. Healy-Rae has left it to him to negotiate on his behalf with the taoiseach and the finance minister. There have been conflicting reports over the past 10 days as to Lowry's intentions and it is clear that the Tipperary North TD, one of the canniest operators in politics, was hoping that Fine Gael and/or Labour would ease the passage of the budget through the Dáil.

With that now unlikely to happen, Lowry has said he is conscious of his national responsibilities. But he won't be neglecting his constituency ones either. He met with Brian Lenihan three times last week and went on Tipperary FM on Friday to reassure his constituents that there would be no cut in the state pension and that OAPs' entitlement to free travel, TV licence, electricity and telephone rental would remain untouched. Lowry had actually nailed down those commitments from the government two years ago in the wake of the furore over the ending of pensioners' automatic entitlement to medical cards.

In terms of the budgetary numbers, they represent small beer but for Lowry, who attracts a strong rural and elderly vote, they could be significant in what is likely to be a highly competitive Tipperary North contest.

Lowry says he won't make up his mind definitively on how to vote until he meets with his organisation – including his seven councillors and his director of elections – tonight. And the likelihood is that both he and Healy-Rae have issues they will want 'clarified' between now and budget day. But the fact that he is in negotiations with Lenihan, and is seeking these concessions, indicates he is serious about doing a deal.

Certainly within government there is cautious optimism that Lowry and Healy-Rae will be on side come the budget votes. And with the old age pension left untouched – for existing pensioners at least – it is unlikely there will be any dissident backbench TDs.

But the cabinet is leaving little to chance. The decision to take the social welfare bill on Wednesday and Thursday surely had an eye to getting the painful cuts passed before deputies had a chance to return to their constituencies, where undoubtedly they will be getting it in the neck.

The outline of the budget has already been painted thanks to the publication of the four-year plan. What we will see on Tuesday is it being coloured it in.

We already know from the plan that personal income tax bands and credits will be cut to the tune of €945m for 2011. The plan revealed that, by the end of the four years, a single person earning €55,000 would pay €1,860 a year, or €36 a week, in extra tax, and it is expected that the budget will look to implement around half that increase in year one. That suggests a worker on €55,000 will see their net pay reduced by around €18 a week next year.

Thousands of workers will be brought into the tax net as the government looks to end the current system in which almost 50% of workers pay no tax. At the other end of the scale, remaining tax shelters will be abolished and there will probably be moves to cap the pay of top public servants – including politicians – and close off a plethora of tax reliefs.

The budget will begin the process of reducing reliefs on pensions. The phased standard rating of income tax relief on pensions will not begin until 2012 but, from next year, there will no PRSI and health levy relief on pension contributions. It almost goes without saying that the 'old reliables' are also facing an increase.

We also know from the plan that capital spending will be reduced by €1.8bn next year and current spending will be cut by €2.2bn – 80% of which will come from the three big spending departments of social welfare, health and education.

This will include a likely 5% cut in all welfare payments, with the exception of the state pension, although it does seem possible that those who turn 65 after 2012 may get less. The very generous tax credits for OAPs are also likely to be cut back and their exemption from Dirt tax eliminated. Health will also take a big whack, with its budget being cut by over €700m – divided between €300m in a reduced pay bill and €400m in services.

There will be some measures aimed at giving a boost to the economy. They will include an ending of the €10 airport tax, although airlines that lobbied against the tax will be asked to deliver additional routes into Ireland to increase tourist numbers.

Any good news, however, is likely to be far outweighed by the bad. It says everything for the mess in which the country has found itself that many people – not least on the opposition benches of Dáil Eireann – will breathe a sigh of relief if and when a budget comprising €6bn of tax increases and spending cuts is passed.

Some things in politics, it seems, don't stay the same.

Cutting it fine - What's in store in Tuesday's budget

# Across-the-board cuts in social welfare – with the exception of the state pension – of 5%

# Child benefit to be reduced

# Big pay cuts for top public servants and politicians

# Abolition of the €10 airport tax

# Thousands more workers brought into the tax net

# Cuts in tax credits and bands, leaving a worker on €55,000 paying up to €18 a week in extra tax

# Reductions in pensions tax relief

# 'Old reliables' to get a hike

# Higher cost of private beds in public hospitals and big savings on the state's drugs bill

# Professional fees to be cut again