I took the iron out of The Beast this morning, and underneath a layer of rust I found a makers mark and some text. It looks as though the iron was made by Peugeot. I did a bit of digging online, and from the style of the logo, it was probably made sometime between 1858 and 1900. Apparently, the lion and arrow logo was abandoned by Peugeot at the beginning of the 20th century, and although it made a reappearance a decade or two later, it was always depicted within a shield of some kind.
The text below the logo, ‘A GARANTIE’, is fairly self-explanatory, but the text above is largely obscured because decades of iron adjustment, presumably with a hammer, has rolled the metal down over it. It might say ‘PEUGEOT FRERES’, which was a trade name used by Armand Peugeot and his cousin Eugène in the 1860’s, and would fit in with time frame of the logo.
This of course says nothing about the age or provenance of the plane itself, which has no markings on it at all. But I understand that it was quite usual in 19th century Europe for plane irons, rather than plane bodies to be stamped with the makers mark.
I suspect that this will be all that I can find out about this plane, but I’ll post back if I find out anything else.