Ironically, Dirty Old Town is not an Irish Song. In fact, it is about an English town. However the song's association with The Dubliners and The Pogues has resulted in many many people tending to think of it as an Irish song.
The town is popularly thought to refer to Belfast, Dublin or Derry. In reality the song was written in reference to Salford, in Lancashire, England. The Pogues are a Celtic punk band from London, formed in 1982 and was fronted by Shane MacGowan.