Would it be more accurate then to refer to the Irish as Gaels, Ancient British as Britons/Brythonic and leave 'Celt' for the more European based cultures?

Orkney, Island of Skye, Man, etc. Perhaps even Bretagne (little chance though).
As far as I'm aware, those locations have large amounts of 'Viking' blood so it'd be hard to find a true 'celt' amongst them.