"This film has been approved for A (Adult Audiences)"

I've seen this title card on a number of British films from the '30s and '40s. In the UK they did indeed have a letter-based rating system at the time, but there was no equivalent system adopted in the US until the late 1960s.

Meanwhile, the Hayes Code applied only to Hollywood product. You'll find that films made in England during this time are generally more liberal about language ("hell" and "damn" get tossed around, as well as ethnic slurs) or about sexual situations that were glossed over in the era's Hollywood movies.

On the other hand, the Brits were more prudish about horror films. The Hollywood horror movies of that time, which look so tame to us now, were usually given the equivalent of an "X" rating, which meant no children were allowed. I recall hearing that even the 1939 Wizard of Oz was given this rating, because the British censors were concerned the Witch would scare the kids!