The London Eye (L) is lit up in the colour green in celebration of St Patrick’s Day, in central London, on March 17, 2011. Meanwhile half a million revellers thronged Dublin, Ireland for the main St Patrick’s Day parade on Thursday in a bid to banish their austerity gloom as US President Barack Obama announced he would visit Ireland in May. AFP PHOTO/CARL COURT (Photo credit should read CARL COURT/AFP/Getty Images)