The UK is and always has been in Europe. When sea levels were lower, just 10,000 years ago, we were joined to mainland Europe by land.
The UK is between Ireland and mainland Europe and even Ireland (and the eastern side of Iceland for that matter) is in Europe.
Whether we are in a political/trading group with other European nations is irrelevant.
We are in political/trading groups with the Commonwealth, but we are not in Asia, Africa, Australia or North America.
As for the current British obsession with leaving the EU, that will fade once the Brexiters realise that nothing has changed w.r.t. immigration apart from the language spoken by the immigrants. After the upcoming Hard Brexit we are going to be substantially worse off than before, and that is before we get screwed over negotiating trade agreements with the USA, China, Japan, and other major trading partners.
But perhaps we'd better leave that discussion for somewhere else as I was born a European, still am a European (UK & Luxembourg Citizen) and will die a European. In my opinion Brexit is the worst decision this country has made since the end of WW2.