Thanks Xracer, just what I was looking for!
I really need to take some pics of it and will as soon as I can get my hands on a digicam. It looks to me like a military rifle because of the plate but.....I don't honestly have a clue.
I searched the net some more after posting and found a gun nearly exactly matching mine on this auction site:
My serial number is 4041F (from memory) and has the same B with the crown markings here and there. The cartridge housing has the number 05 stamped underneath. Unlike the one pictured it has no rubber butt plate but it does have strap loops.
The sight on mine has exactly the same side profile but has a raised horizontal 3 inch long rail with increments that protrudes from it facing rearwards. It raises and lowers as its adjusted in/out using a spring loaded slider.
Unfortunately mine is missing the actual bolt.