@Helen - in answer to your questions, she says she was playing in a ceilidh band in Joburg, South Africa, and this tune was part of the repertoire.   They would have been playing medium sized halls and pubs, sometimes as wallpaper for diners, sometimes for dancing.

One might say that therefore it's likely the tune is not Irish, but I think the opposite is true ... the colonies (I grew up there) are more fanatically 'proper' about that kind of thing than the British are.   No band styling itself as 'Irish' would dream of including anything that wasn't Irish, or British Celtic at the very outside.

Of course, this is only my opinion, so the possibility remains that the original tune is not Irish, but I wouldn't attach too much weight to it.

The wife, in a moment of inspiration, remembered the band leader's name and said he would know immediately, so she's gonna try and track him down.

@Stanron - thanks for your contribution :).   It looks pretty good at sight, but I'll have to take a while and work it out.    The fact that everyone seems stumped as to what tune this is makes me think it might be one of that band leader's originals.    The thick plottens.