Are comma splices more common in British English or American English?

In the late 1960s/early 1970s there was a fad among educationalists in England for not teaching grammar. I was at school at the time this fad became official and I remember certain teachers saying things like "the new idea is that we are no supposed to teach grammar but..."

The idea was that pupils should just pick up correct English usage naturally by hearing it spoken and that formally teaching grammar was unnecessary and artificial.

There is something in this of course - you don't need to know all the highly technical classifications used in formal grammar in order to speak and write correct English, but...

You can't simply not teach any grammar at all because, if people just rely on copying how others speak, wrong usages gradually creep in. Obviously you need to know some formal rules of grammar so that when you hear usage that doesn't sound quite right you have the tools to work out whether it is or it isn't.

But, like many educational fads, it was taken to the extreme and has resulted in a general lowering of standards of English usage.

Any parent who has children at school will receive letters from the school which are poorly written and grammatically incorrect. The spelling is always fine (spellcheck!) but there are errors of grammar. And poor standards of literacy among teachers obviously perpetuate poor standards in society generally including in official publications from government, councils etc.

If you find this hard to believe just look at the Department of Education website. For example https://getintoteaching.education.gov.uk/a-day-in-the-life-of-a-teacher

Teachers usually stay at school for a couple of hours to do marking, planning, admin, or contact parents about any behaviour issues. Some days, the school will have staff meetings or professional development time after the children have gone home.

Some teachers may do some marking or planning over the weekend, but others may choose to fit everything in the working week.

So that is why comma splices are more common in England - standards of literacy in England are in decline.