Irish Nationwide has described an e-mail sent by the son of chief executive Michael Fingleton as 'inappropriate and regrettable in the circumstances'.

The e-mail was seeking deposit business in Britain on the strength of the Government's move to guarantee deposits in the Irish banking system.

The Financial Regulator said it was looking into this matter. 'It is inappropriate to use a guarantee in marketing, advertising, or in any communications to customers or potential customers,' it said, adding that all firms had been advised of this.

Michael Fingleton Jnr sent the e-mail to a friend from the Irish Nationwide's London office stating that Irish Nationwide represented the 'safest place to deposit money in Europe with an AAA guarantee from a country with the lowest national debt to GDP ration of any AAA country'.

The e-mail said that deposits attracting fixed term interest rates of 6.75% and 7.1% were guaranteed regardless of size and represented the best value in the UK market. The e-mail continued: 'Please be so kind as to pass on to friends, colleagues and clients as you see fit.'

The terms 'guarantee' and 'guaranteed' are used six times in the e-mail. This term is particularly sensitive because of the negative connotation implied for the British banking sector which is not subject the same level of Government guarantee as the Irish-owned banks.