Have you tried intelli-mirror?  That's the situation it was meant for.  Note that your preview will look the same as what you pictured because the "intelli" part is not calculated until print time, so you would have to turn on print preview in the driver and actually print it and look at the driver preview to see if it is working the way you expect before you print.

Regards,
Mike

G'day Mike,

Sorry for the slow reply. Christmas & New Years holidays and all that stuff. (But that's all the days off I get until Christmas 2022!!)

Intelli-mirror was the first thing I tried before I posted in this forum. It certainly worked perfectly along the bottom edge of this particular image, and the left & right sides wer fine too, but along the top edge of the image (where there is really only a VERY small amount of detail) it struggled. It ended up leaving quite large digitised smear marks (for want of a better description?)
I've attached images of the top edge for you to see. Interestingly, the preview screen in Qimage did not show any of this smearing, it only became apparent when the image rolled off the printer.

Ideal world?
Intelli-mirror along the bottom edge, standard mirror along the other 3 edges. 

I know......... I'm not asking for much, am I?!