"Why should the UK come to the aid (and vice-versa) of Europe should it be necessary in the future"
Well
a) its 22 miles away - sadly true, but across water that has held petty dictators at bay in the past (all of whom have been European....)
b) 43% of UK exports go there - no longer true, and even when it was, included exports routed to non-EU countries via Europort.
c) ever since Tudor times the English have fought to stop one country ruling Europe - possibly true, but no longer a sustainable strategy now the eurotrash all want to be one country.
other than that I guess there's no reason at all...........................
If the Russians invaded Europe, I would pour a beer, grab some popcorn and watch the show from the white cliffs of Dover.