Identifying more with being English/Scottish than British is indeed an interesting concept and again is something I have heard quite often. It's hard to conceptualise every nuance such as that in simple quantitative measures however.
If you are hearing it quite often I think you should listen. It is not so much an interesting concept or a nuance as fundamental to how you define Britishness. IMO the issue needs tackling head-on and shouldn't be dismissed as "too hard", especially at PhD level.
Saying this for your own benefit - presumably you don't want to antagonise your examiners.