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

Thoughts?

According to several music dictionaries:

A tempo or Tempo Primo as follows,
A tempo is the music direction which means to return to the original pace of a song. (adverb)
An example of a tempo is when the music returns to the slow pace experienced at the beginning of the song.

In another it says:
A Tempo -Resume normal speed.

In another it says:

adv. & adj. Music ATempo-
In the tempo originally designated; resuming the initial tempo of a section or movement after a specified deviation from it. Used chiefly as a direction.

So sounds like it depends on whether or not there was various deviations from the original speed, if the piece is seperated into "movements" I can't remember that with any Grade 5 pieces that there are clear movements but it might be that there are clear sections within a piece. Maybe the examining board have guidance somewhere, sometimes they do make mention of specific instructions and how they are to be interpreted in the study book.
Hope you can get the definitive answer, though maybe not by the time of the exam!

I usually take it to be that 'a tempo' in italics is a return to the speed of the section before 'rit' or other temporary tempo marking, whereas 'a tempo' in bold is the return to the beginning speed.

That would very much depend on the house style of the publisher or engraver. In this case, the ABRSM put all tempo marking in bold, including the preceding 'Poco a poco allargando'.

I don't expect to get one, given that the composer is dead!

Actually I meant from the ABRSM regarding their expected understanding of the term used in their examination pieces.