I picked this item up off ebay recently, and am very surprised at how little is documented on a brand that crops up on a pretty regular basis. A google search throws up very little in the way of meaningful suggestions as to manufacturer, and even Hull's book on English pens omits this model.
My best guess, based largely on the shape of the section, is that this was a product out of the Mentmore factory. Any one able to throw light on to who produced what seem to have been better quality pens?