"In RP, do I say After or AHfter?" 

Have any of your students ever struggled with this one? 

Here's a little tool that will bring some clarity to this question...
It's called the "ASK LIST." This is basically a list of SHORT A VOWEL words that change to "AH" in RP and Cockney accents! I've created a simplified version of the ASK LIST for you!

Download Adam's The ASK LIST