Hi Seasons,

If I had to hazard a guess, I'd wager that higher Great Britain and Ireland results (which used to all be lumped together as "British Isles" before), indicates descent from the original Celtic-speaking Britons, Picts, and other Celtic-speakers of Britain and Ireland before anyone else invaded and settled in Britain (i.e. Romans, Anglo-Saxons, Vikings, Normans, etc.).

Scandinavian admixture is so high in Great Britain because of the Anglo-Saxons, Vikings, and also Normans (who were a Scandinavian/French blend).

So, I'd think your ancient ancestry is largely native Celtic British with some admixture from the later Dark Ages/Medieval invaders/settlers such as Anglo-Saxons, Vikings, or Normans.