Its a Brockhouse SPRYT 2-stroke engine as fitted in the BMB “Hoemate” 2 wheeled garden tractor of the 1940,s / 1950,s.
They are cracking little engines (well I like them anyway :):)).Have you got the alloy engine cowling as you must not run it without it fitted !!
I have a complete BMB Hoemate plus a couple of spare engines.One of these engines requires a replacement big-end bearing assy (actually they are individual rollers made from steel and bronze) and crankpin.