The actual production dates for the model 150C is 1957 to 1961.

As already proven, my memory is not the gold standard for reliability, even so, I venture to say that a 150 grip frame without a textured paint is never seen on an US produced 150 of any sort. However, Crosman Canada certainly produced 150s with smooth paint (Crosman Canada seemed to do whatever the heck they wanted with some very weird results) that combined with the Brown grip (US 150C always had black, as far as I can recall ever seeing) strongly suggests that this is a Canadian 150C.

What would go towards confirming this would be if a couple more examples like this in the UK could be found.