I have two friends.
One born in London to English parents, raised in Glasgow & a staunch Rangers fan, speaks with a broad Glaswegian accent & identifies as Scottish.
Other bloke, born in Rochdale of Scottish Parents, speaks with the same accent as me. Staunchly Scottish.
Basically its down to cultural exposure, you are what you feel yourself to be.
Me? Scottish & Welsh heritage on my maternal side, but i know/feel naught of that. My fathers side have been here since before the Conquest, we are in the Domesday book & our name comes from a place four miles from where i sit now. Guess which side i identify with?
My maternal grandparents were all miners who moved from Wales/Scottish borders to look for work in the mills in the C19th, but i know almost nothing if them as people, which is a real pity. I dunno, how do you quantify a feeling?