2♦ was reverse Benjamin, showing an Acol strong two in any suit or a strong balanced hand.
You are playing standard (for England) carding methods. You normally play high to encourage on partner's lead of the ace, but also agree to play suit-preference signals if dummy has a singleton in the suit led.
[Edit:] North led ♦A
What card do you think South should play to trick one? What signal do you think this will convey to partner? Any other comments?