This is a small engine from the range of interesting steam engines made by Ben Peake.
To quote the maker's manual:
MINOR is the smallest of the engines that are made in the Peake workshop. It is a single acting oscillating steam engine made of Stainless Steel, Brass, Copper and a piece of Oiled Pine. Listed below are the specifications of this charming little engine:
Stroke Length 7mm (0.28 Inches)
Bore 4mm (0.16 Inches)
Flywheel Diameter 17.5mm (0.69 Inches)
There may be some variation in these measurements as these engines are carefully handmade in small batches.
There's little I can add to that, except that the minor is no longer "the smallest of the engines that are made in the Peake workshop". Ben has since made the micro and the nano which are both even smaller.
The bottom picture on the left is a scan of a "Certificate of Authenticity" quoting serial number 51. As far as I know, however, it is not a limited edition.