Rare halfpennies and farthings were issued from Dublin in 1339/40. According to the O'Brien coin guide: Edward III issued farthings and halfpennies for Ireland in 1339-40 but they are exceedingly rare – only one farthing is known and two (possibly three) halfpennies exist. A third Irish halfpenny of Edward II has been found in Hampshire and is being authenticated by the experts at the Portable Antiquities Scheme (PAS) in the UK. It has been initially described as: A very worn 14th-century debased silver medieval Irish halfpenny of Edward III, 1339/1340 coinage, struck at Dublin mint (1339-1340 AD; Spink 6269). The coin has suffered some circumferential losses. The wear is differential on the surfaces with the reverse surviving far better.
The Irish coins of Edward III are easily mistaken for those of Edward I – especially if in poor condition. The key distinguishing difference is that the obverse legends spells out Edward’s name fully : EDWARDVS REX rather than the abreviated form that occurs on the issues of Edward I