Hope this works, Picked up one of these last week, see if Grant knows what this odd mark is. Fuzzy I know, stamp reads "WDC RA 191"
The "D" could be an "O", and the "R" could be a "P", but i'm pretty sure they're not.
The numbers all match, and all the other Royal acceptance marks are there, along with broad arrows on everything. No out of service marks though, and no civilian proof ratings stamped on it. Just in front of the forcing cone on the left side is " and" which I believe is a badly stamped "England".