Arguments have been bouncing back and forth recently over the relative merits of voting for or against the Nice Treaty. As polling day approaches many remain confused about the likely repercussions of voting Yes or No.

Is it, as Mr Mick O'Reilly of the ATGWU has asked, "Nice or nothing?" or a matter of Nice or something better or indeed worse? Or is it as simple as Mr Alan Dukes of Fine Gael would have it - that a Yes vote is as obviously good for the State as was joining the EEC in 1973? The economic arguments for a Yes vote centre around the benefits of enlargement. The 12 candidate countries have a combined population of more than 100 million people adding to the 375 million already in the EU. This is a huge market for Irish firms, although one that is, to some extent, already open.

Of course, it will be some time before all of these states join. But without the Nice Treaty, not all of them could do so. There is some debate about whether five countries could join under the provisions of the Amsterdam Treaty. Even legal opinion differs with some arguing that the need to amend the voting structures in the old treaty rules out any enlargement until this is done.

But it is not just trade advantages which AIB's Mr Michael Buckley in particular has pointed to. There is also a labour market bonus, he says. So far it is unclear how quickly the people of eastern Europe would be able to work here. The EU is looking to block labour from candidate states for two years following accession, with reviews allowing for a bar for up to a further five years. It is possible Ireland, should it wish, could allow workers in without the red tape necessary for work permits. For the moment, confusion reigns. There are also implications for foreign direct investment. On one side there is the argument that an enlarged EU will be even more attractive to foreign multinationals. Ireland already has a headstart in attracting these firms. Some argue that the far lower cost economies of Eastern Europe will pick up much of the investment and that Ireland will have to seek out more value-added processes. This is probably the result of globalisation and is likely to happen with or without the Nice Treaty.

There are other economic worries, chiefly associated with the future of taxation policy. Some European leaders have made it clear in recent times that Ireland's low corporate tax regime is firmly in their sights. The Taoiseach, with the aid of the British, may have fought off attempts to get taxation included in qualified majority voting in the Nice negotiations last December but it is unclear that the exemption is unassailable.

Even the Commission taxation commissioner Mr Frits Bolkestein, in Dublin last week, drew attention to the possibility of using the "enhanced co-operation" parts of the Nice Treaty to advance harmonisation in taxation policy. There are fears that a number of larger countries could decide to go ahead with corporate tax harmonisation among other issues.

Ireland could stay outside this but the question is, if the choice is between the slow lane with low tax or the fast lane with higher tax, which will our politicians choose?

It is this provision for enhanced co-operation which persuaded the Government a referendum was needed as this is a completely new departure for European treaties. Enhanced cooperation was only introduced to the agenda in 2000 well after much of the rest of the treaty. It allows up to eight member-states to go ahead with certain policies without the rest, although none can be excluded.

According to the treaty, enhanced co-operation should not be used in the single market, the common agriculture policy, competition policy or economic and social cohesion. However, Mr Bolkestein's assertion that cooperation could be useful in taxation policy, raises a question over this. So what actually happens if a Yes or a No vote prevails? According to Ms Brigid Laffan, UCD's Jean Monnet professor of European politics, a No vote would provoke a ratification crisis and a crisis in Ireland's relationship with its partners and the candidate countries. "A No would be interpreted as a No to enlargement and a No to the historic reintegration of the European continent. Rightly or wrongly, the Irish would be portrayed as a people who supported the EU while the financial benefits flowed, but refused to show solidarity with our neighbours to the East."

The Government would have to find a new solution.

To date the EU has never reopened negotiations on a treaty. In 1965, French president Charles de Gaulle wanted to alter the Treaty of Rome but he was refused. The same happened to the Danes in 1992 post-Maastricht, when Denmark was merely given a protocol. This clarified the opt-outs it had negotiated and allowed the government to persuade the electorate to vote yes in the following referendum.

A No vote would result in a lot of serious work for diplomats to allow some revision which would permit another referendum But the difficulty would be in deciding why people have voted No. Is it worries over taxation and democratic accountability or is it worries about the Rapid Reaction Force or something else altogether, such as the loss of a guaranteed commissioner?

Irish diplomats in Brussels also warn that a negative result will lower the influence of current commissioner Mr David Byrne in the eyes of his colleagues. European insiders suggest the "strength of [the] Yes vote over [the] last 25 years has given moral strength to all Irish commissioners at [the negotiating] table and [it is] well known that Ireland is pro-Europe and as a result Ireland has punched above [its] weight. If there is a No vote, the problem is that the moral authority of the commissioners and officials negotiating would be gone and [there would] be no sympathy whatsoever for any special treatment Ireland wants on any issue."

A Yes vote, for the time being, would effectively maintain the status quo. In time, it will mean there will be times when Ireland is without a commissioner. This will happen once all 12 applicant counties have joined. It also means a lower representation in the European Parliament and fewer votes at Council level. The larger member-states have picked up proportionately more here to make up for dropping their right to two commissioners.

But perhaps most importantly, it will legislate for enhanced cooperation. No one is sure yet quite how this will work or indeed what policy areas are likely to be targeted first.

Certainly Ireland will want to play a key part in this and, if the vote is Yes, there will be a need for a proper debate on the future of the EU and how best to influence the debate in Europe to our advantage.

Series concluded