Has something irremediably nasty finally stuck to the Teflon Taoiseach? When announcing his unexpected resignation as Ireland's Prime Minister yesterday, effective from next month, Bertie Ahern insisted he had never received a corrupt payment and had not dishonoured any office he had held. Many remain to be convinced, as the findings of recent opinion polls on his credibility and trustworthiness have confirmed (both show him enjoying the backing of only half of the electorate).

Mr Ahern's resignation suggests that he has lost his non-stick coating after nearly 11 years as Taoiseach. This week, he began a high court challenge in Dublin to limit the scope of a public inquiry, the Mahon tribunal, into alleged corrupt payments to politicians in the 1990s. Mr Ahern has been damaged by evidence given to the tribunal about "dig-outs", undeclared loans or gifts from friends when he was separating from his wife and looking to buy a house. Other evidence, concerning the way his personal finances were managed when he was Finance Minister and the matter of a deposit he maintained was an Irish parliamentary salary cheque but was, in fact, a payment in sterling of £15,000, has also been as embarrassing.

Mr Ahern's explanations have been unsatisfactory and evasive. Given his stated desire to ensure that the minutiae of his personal financial circumstances do not dominate the Irish agenda to the detriment of the issues that count in the long term and need to be addressed as a matter of some urgency, he was probably right to resign. He can now concentrate on his legal action and hope that the body politic can focus on what matters in Ireland. This has a resonance for Scotland, Britain and the European Union.

Alex Salmond, the First Minister, has made much of Ireland's economic miracle, arguing it is a success story that could be emulated by Scotland if independent. The narrative looks less convincing, with potentially damag- ing consequences for the SNP, given Ireland's economic problems. The challenge now for Dublin's coalition government is to manage a transition from high to low growth. Ministers warn of tougher times ahead. If the Celtic Tiger has been tamed, it will hold less appeal for Mr Salmond and be less persuasive for Scots in the run-up to a possible referendum on independence.

Mr Ahern's departure will come weeks before a likely Irish referendum on the Lisbon Treaty. Ireland is the only country among the 27 member states committed to a referendum and if the treaty is rejected (as happened to the Nice Treaty in the first Irish referendum of 2001) by just one country, it cannot come into force. The past volatility of public opinion on this matter suggests that a stable political environment in the run-up would be infinitely preferable to a period of instability caused by the Taoiseach's resignation amid allegations of financial irregularities.

Yet instability is likely to be the reality and this could be damaging for the credibility of the EU should the situation contribute to a winning no vote. This would also have repercussions for Gordon Brown as it would raise anew the thorny question of a British referendum when he hoped he had put the matter to bed with a majority in the Commons agreeing that the treaty was not an EU constitution by the back door. Probably the least problematic repercussion of Mr Ahern's resignation, from an external perspective, concerns Northern Ireland. Soon three of the men who did much to return power-sharing to Stormont will no longer hold high office: Mr Ahern, Tony Blair (who has gone) and Ian Paisley. There is always the risk of an abhorrent political vacuum when big-hitters leave the stage but the fact that power-sharing looks here to stay must greatly minimise that risk in Northern Ireland. If history is to be kind to Mr Ahern, it will perhaps be for his role in Northern Ireland above all else. Ignoring for the present his personal troubles and their possible implications on this side of the Irish Sea, that would be a positive legacy.