Here are a couple of links to help you with part of your question : the part about your celtic cousins.
Welsh
http://www.plaidcymru.org/
Scots
http://www.snp.org/
Though I should point out to you that the majority of Scots are descendants of Vikings as well as Celts similar to the English.
Small groups of people have to unite against the majority and in being unified they become stronger than the majority. Most English people don't do that. In many cases they feel other affinities are more important. For example many people in northern England feel a greater affinity to those north of the border than to Londoners. Other things to taken into account are regional accents which also have a binding / separating effect.

I think it's a matter of confidence.
Only the insecure and inadequate are concerned with the obsessions of others.