British "Rule Of Wind"???

[Steinar]

Never heard it before.. Nor did I find anything on Google.

This is my wild guess ;
Perhaps it's another description of the vector wind effect we have for long range shooting?
E.g. for right twist barrels; wind from 9 o'clock gives an impact down at 4:30 and wind from 3 o'clock gives impact up at 10:30.