The Irish are, not sure about the Scots.
The dictionary isn't much help either: Celts
1. One of an Indo-European people originally of central Europe and spreading to western Europe, the British Isles, and southeast to Galatia during pre-Roman times, especially a Briton or Gaul.
2. A native speaker of a modern Celtic language or a descendant of such a speaker, especially a modern Gael, Welsh person, Cornish person, or Breton.