I suspect it may be more the case that many people under 40 in the UK weren't really taught much at all in the way of grammar, and even people who have involunt

I suspect it may be more the case that many people under 40 in the UK weren't really taught much at all in the way of grammar, and even people who have involuntarily picked up fairly decent grammatical skills still struggle with comma splices, which are, admittedly, quite a subtle sort of error whose detection is predicated by a full mastery of the purposes of the various punctuation marks and an understanding of clauses.