For more than a decade the Greens have been a party of government in several European countries. Jamie Smyth, European Correspondent, examines their record
Since the Green League in Finland grabbed a seat at the cabinet table in 1995, a succession of Green parties in Europe has joined coalitions, transforming what were initially environmental protest movements into serious contenders for power.
The Greens are in governing coalitions in Italy, Latvia, Finland and the Czech Republic. Over the past decade they have also played a role in federal governments in Germany, Belgium and France as well as assuming power in local and regional assemblies in many parts of the European Union.
But going into government has not always proved easy for the Greens in Europe, many of whom have been criticised by their own supporters for "selling out" their principles in pursuit of power. Perhaps the best example of this was in Germany, where Green leader and foreign minister Joschka Fischer became embroiled in a bitter internal party dispute about whether the government should actively support Nato-led military action in Kosovo.
"We didn't compromise our principles on this issue, rather we clarified our principles," insists Reinhard Bütikofer, chairman of Germany's Green Party. "We are not a radically pacifist party . . . we decided to oppose genocide in Kosovo."
Yet many rank-and-file Green Party members disagreed with what was Germany's first combat deployment since the end of the second World War. Bütikofer estimates that 5 to 6 per cent of the party membership left after the divisive internal debate between one wing, which favoured government, and another wing that favoured sticking closer to core principles while in opposition. But it was necessary, he says.
The bruising experience of being part of the first Red-Green coalition in 1998-2002, which involved internal debates over military deployments in Kovoso and Afghanistan and the phasing out of nuclear energy, did not hurt the Greens at the ballot box.
It also represented a "maturing" of the party after years of opposition.
"Ten years ago no one would have even bothered to speak to us about forming a coalition and in business circles we were considered irrelevant. The most important change is that we gained respectability in power without losing our core support."
Whether the German Greens were able to make any substantial changes to policy is debatable. Daniel Mittler, a political adviser to Greenpeace International in Berlin, says the Red-Green coalition achieved some notable successes, such as a new law boosting funding for renewable energy projects. But he says the party also made too many compromises with the nuclear industry and did not fundamentally alter the economy because it favoured road transport and the building of new airports.
In Finland the issue of nuclear power - the traditional enemy of the global environmental movement - forced the Green League to exit government in 2002. It objected to the coalition's support for a proposal to build a fifth nuclear power station and decided to relinquish its place in the ruling coalition after seven years rather than compromise its own anti-nuclear stance.
The party has steadily increased its vote following the decision, and recently joined a centre-right coalition, despite the other party's continued support for existing and perhaps new nuclear power stations.
"If industry brings its proposal to build a sixth nuclear power plant it could be difficult for the Green League, although they have been careful not to say that it is a coalition-breaking issue for them this time," says Richard Brander, a political analyst working at the largest Swedish-language newspaper in Finland, Hufvudstadsbla.
By adopting a flexible attitude towards nuclear power, the Green League is following the example of several Green parties that swapped the opposition benches for the cabinet table in pursuit of influence.
The French Greens, les Verts, joined Lionel Jospin's coalition, which maintained France's staunch support for nuclear energy.
In the Czech Republic the Green Party has also swallowed its pride on the nuclear question by joining a centre-right coalition with the pro-nuclear and eurosceptic ODS and Christian Democrat parties.
Taking a tough stance in coalition talks, the Greens got three cabinet posts for their six members of parliament. They also extracted an agreement that no new nuclear units would be built at existing plants. But their commitment to the coalition is currently being tested by the debate over the location of a radar station for the controversial US missile defence system for Europe.
"We are not completely against it but we feel the plan lacks co-ordination with Nato and the EU and has not sufficiently been discussed," says Czech Green MP Ondrej Liska.
"But we have agreed to lead talks between the Czech government and the US to see if it is possible to bring the strategy under a Nato or EU defence system."
In an Irish context, the debate over missile defence could be seen as a close parallel to the use of Shannon airport by US troops. In opposition, the Green Party has railed against the practice but in government would it be forced to take a softer line to protect Irish-US relations?
The party would also face difficult decisions in health, economic and energy policy as the price for places in government. The party would probably have to re-evaluate its position on Europe - the Greens were the only mainstream Irish political party to oppose the Nice treaty - and one of the first big tasks of a new government would be to renegotiate and attempt to ratify the proposed EU constitutional treaty.
The question is how far the Greens go without the party losing its soul?
"There is no general rule on when a compromise is acceptable to stay in power," says Monica Frassoni, co-president of the Green group in the European Parliament.
"Once you make sure that your role in that government will be one to diminish the damage that otherwise would be done and if you make clear as soon as you enter an alliance that you will not change your conviction . . . then you can live with it."
Of course Bertie Ahern will also have to make a judgment call on the Greens. Will it stick to a programme for government? Ahern will have to be persuaded that the Greens are ready to follow their German cousins into the mainstream by trading in their sandals to get a grip on political power.