Ireland's decision to prop up its six biggest lenders by agreeing a €400bn (£313bn) financial package that guarantees all their debts and deposits was passed into law yesterday, despite an outcry across Europe about the impact that it would have on the EU's single market.
British bankers have said there are already signs that companies and wealthy individuals in the UK have been the subject of aggressive marketing campaigns by Irish banks.
Irish banks are targeting customers who are more likely to have cash balances in excess of £35,000, the point at which the UK government no longer guarantees deposits. That limit is to be increased to £50,000 in the near future.
Yesterday, tens of thousands of savers transferred money from the UK to accounts run by Irish banks, including Post Office accounts run by Bank of Ireland.
The Financial Times today accused Ireland of "economic nationalism" and said that the Irish government "has behaved anti-competitively and the protection it is offering could even destabilise other banks".
Brown has raised his concerns with Brian Cowen, the Irish prime minister, in an attempt to stamp out the problem and avoid an public row with Ireland.
However, Brown's move maybe too to stop the exodus of business.
Yesterday, Irish Nationwide, the Irish building society, approached City workers through an e-marketing campaign, which emphasises government guarantees and attractive interest rates on bonds.
In an email to employees of a large investment bank, Michael Fingleton Jr., an Irish Nationwide executive, wrote: "We now represent the safest place to deposit money in Europe with a AAA guarantee from a country with the lowest national debt to GDP ratio of any AAA country."
The first three days of this week have seen three times the normal level of new accounts and inquiries about Irish banks, according to price comparison website moneysupermarket.com.
It said Irish institutions accounted for 25% of all the savings-related traffic to the site. The problem is also being exacerbated by the decision of Northern Rock this week to close accounts to new customers, to prevent a breach of competition regulations.
As a nationalised bank, Northern Rock offers 100% government deposit protection, but it was forced on Wednesday to close its e-online account and five others, to avoid attracting more than 1.5% of total UK savings.