I did a bit of googling since making that comment, apparently it is in the American south.
I really hate how fascists keep stealing symbols. I believe they've been doing it from their inception. I believe I read a while ago that even a variant of the Celtic cross had also been used as a hate symbol as well.
Personally my mentality is "don't let them have it". If fascists use a symbol, in many cases we should continue using it so their attempt at hijacking it fails.
Although I still wouldn't really associate the Jerusalem cross with the UK, moreso just generally a symbol of historic/traditional Christianity