Pangur Bán
Deconstructed
@Traitorfish, you may be overstating the case. Opening lines of Caesar's De Bello Gallico start by defining them as a lingustic group and differentiating them from Germans, though differentiating them also from Belgae (related group) and Aquitanians (proto-Basques).
You should read Murray Pittock's Celtic Identity and the British Image and some of his other works. Celticness as a romantic identity is a proxy for resistance to Britishness, so is viciously attacked by proponents of Britishness in a variety of forms, including the counter-myth (framed as myth-busting). As a result, there are lots of establishment 'myth-busters' saying all Celticness is invented and such stuff, but actually it is usually fairly easy to tell the difference between Roman- and post-Roman-era Celtic-speakers and Germanic speakers based on names (e.g. personal names, Calgacos (swordsman) or Argentocoxos ('silver leg') versus Sigeric (victory+wealth/authority/ruler) or Alaric (everything+wealth/authority/ruler)).
You should read Murray Pittock's Celtic Identity and the British Image and some of his other works. Celticness as a romantic identity is a proxy for resistance to Britishness, so is viciously attacked by proponents of Britishness in a variety of forms, including the counter-myth (framed as myth-busting). As a result, there are lots of establishment 'myth-busters' saying all Celticness is invented and such stuff, but actually it is usually fairly easy to tell the difference between Roman- and post-Roman-era Celtic-speakers and Germanic speakers based on names (e.g. personal names, Calgacos (swordsman) or Argentocoxos ('silver leg') versus Sigeric (victory+wealth/authority/ruler) or Alaric (everything+wealth/authority/ruler)).