A nice example of the Wm Marples & Sons X4 smoothing plane produced between about 1954 and about 1965. It was advertised as not recommended for the "Do it yourselfer". Marples apparently had high expectations for the plane and touted it for the more professional user.
Roughly based on the Bailey design, the plane has some significant differences, largely cosmetic but a few practical improvements over the Bailey.
As with many British made planes, the heft of the X4 makes it easier to use with less effort needed to push across the workpiece. The frog and tote are a combined unit and manufactured out of wood. The iron has a unique curved top and the lever cap is hinged at the top and let lever is shaped to accomodate the fingers.
Excellent performance and easy adjustment make this a fine user, though its rarity and value would preclude it from a bench worker. (that is unless you fancy a rare plane for your projects)