The screw driver existed in 2 different versions. The early style was a fixed flat blade C. 4585, same as for XK 140 and 150, which was replaced at car. No..’s  850648, 878937, 861071, 888139 with the combination screw driver C.20482.  Very easy to distinguish. The early style has a fixed single blade, a slightly larger handle and the JAGUAR is written on the outer surface. The later style has the combination of 2 blades, one Phillips and a conventional blade. The handle is somewhat smaller and the JAGUAR is written in the recess. Be careful as of the later type are already some reproduction available which actually have  thinner blade shafts, the handle has no line around the JAGUAR.

Screw driver explained in a video

Study pics