Blockchain.info just added the ability to use Barclay's Pingit to buy bitcoins using GBP:

 - https://blockchain.info/wallet/deposit-pingit


You can also send cash (GBP) in the mail to Bitcoin Nordic (in Denmark):

 - http://www.BitcoinNordic.com


And, or course, there may be a chance for a local trade:

 - http://www.LocalBitcoins.com


Ireland uses SEPA, so there are alternate methods, including:

 - http://www.BITSTAMP.net
 - http://www.Intersango.com
 - http://www.Bitcoin-Central.net
 - http://bitcoinsinberlin.com
 - http://www.MtGox.com
 - http://www.BitcoinNordic.com