The flagging campaign against the Nice Treaty in the Irish Republic suffered a setback yesterday when one of its most prominent spokesmen was reported to have links with an extreme right-wing German party.

Justin Barrett, who fronts the "No to Nice Campaign," was said to have attended a fascist-style rally mounted by a party that German authorities believe has "Nazi characteristics". Although his organisation is among many advocating a "no" vote in next Saturday's referendum on the Nice Treaty, he has been to the fore in the intense campaigning on the referendum.

The reported links will be most unwelcome to anti-Nice activists as the hotly contested campaign enters its final week. One issue concerns a possible rise of migration into Ireland if the Nice Treaty is ratified and eastern European countries are admitted to the EU.

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There have been few expressions of overt racism in the campaign, but there has been much debate on jobs and whether Nice would put jobs at risk, or whether it could increase employment by providing a larger market. Parties such as Sinn Fein and the Greens oppose Nice, as do ad hoc organisations set up for the referendum, but most of these have kept their distance from Mr Barrett, who is known as an anti-abortion activist.

He is said to have threatened legal action against newspapers that examined his background, including the Sunday Mirror. Rumours of his alleged ultra-right views were investigated by The Irish Times, which established he had attended a fascist-style rally in Bavaria. This was organised by Germany's National Democratic party. The German government regards the party as a threat to democracy and two years ago tried to have it banned. The rally gave a standing ovation to a former SS officer and heard speeches lauding and quoting Adolf Hitler.

Mr Barrett was described as an "honorary guest" at the rally by the NPD. Holger Apfel, its deputy leader, said: "We have been in contact with his group since 1996. We are friendly with his Youth Defence organisation." Mr Barrett's said: "This is a smear campaign started by that gutless newspaper the Sunday Mirror and obviously The Irish Times is now working on it as part of this campaign by the 'yes' side."

The No to Nice Campaign generated many complaints when it produced posters showing a young man with a gun to his head, captioned, "Don't be bullied". Whether the gun is held by the man or someone else is unclear. The posters were denounced by the government as offensive, crude and scare-mongering.

A survey shows opinion has swung markedly towards a "yes" vote in next Saturday's poll, with support for Nice leaping from 29 per cent to 44 per cent. But the high number of undecideds, at 27 per cent, means the issue is regarded as not quite cut and dried. The figures seem to show most of the electorate is not, as had been speculated, poised to use the referendum to punish the Irish government. The administration, led by Bertie Ahern, has recently plummeted in popularity.

But all the Republic's largest parties want a "yes" vote, and all have called on voters not to use Nice to attack the government, saying the wider European issue is at present much more important than domestic political concerns.

After a slow start, the "yes" campaign, with the government to the fore, has become more energetic and has apparently successfully countered the arguments of the "no" camp. One of the main issues has been Irish neutrality, with some opponents of Nice saying Europe is stepping towards creeping militarisation, which could undermine traditional neutrality.

The government has obtained a formal EU declaration of the Republic's neutral status, which appears to have convinced some doubters. Next week more intense campaigning is expected, especially by the government, since a rejection would be a huge blow to its prestige at home and to Ireland's standing in Europe.