In the UK they used to go from U (same as the US G), then PG, then 15, then 18. There was no PG13 equivalent. So Gremlins caused a stir when they rated it 15 which ruled out most the family audience.
So in 1989 with the release of Burton’s Batman they introduced a 12 rating (since amended to 12A) which filled the PG13 gap.
Now I have my moan that they rate almost everything that isn’t a kids cartoon or a horror movie as PG13/12A making the rating so broad it becomes almost meaningless.