peoples in guernsey and jersey etc are still British, being British just means that you live in the British isles (including all outer Scottish isles and channel islands) etc...
I do get your point though, on a technicality UK isn't geographically a single country, but politically it is a single country.
I do get your point though, on a technicality UK isn't geographically a single country, but politically it is a single country.