Since encountering this piece, I've always interpreted the A tempo at the end to mean a return to Allegro, as a slightly humourous throw-away flourish, dissipating the preceding energy.
I hadn't listened to the ABRSM recordings, indeed I never do, preferring to look on new (to me) pieces such as this with an open mind. So it came as a surprise yesterday when a pupil told me the recording returns to the slow speed from the very beginning. To me, this makes far less musical sense, and given that his exam is this afternoon, I told him to stick with what we've been doing!
There definitely seems to me a bit of ambiguity as to what is actually meant by A tempo in this context, whereas Tempo primo would clearly indicate a return to the very first speed. For future candidates, I'm going to discuss it, present my case, and see if they can convince me otherwise