GG375, it is an original MS action. Many British rifle makers bought actions from Steyr in the 1900's and then stocked them and stamped their name on them. Examples I have seen are Jefferies, William Evans, Purdey and Gibbs. The greek military ordered a load of them from Steyr, who, as far as I know, continued to manufacture the action until about 1970 when it became cost inefficient.
They were always very expensive actions to produce. I will be having a new "butterfly" swept back
bolt handle made, not too much of a sweep though, I like the "medium" ones

best, Mike