There are a number of subtle differences in the various vintage Whitworth's. I purchased mine new in 1984 and it has a different shaped bolt handle, cross bolt style, front sight and different stampings, especially note that this one states "calibre", English style. Mine simply says Cal. 375 H&H Mag like most I have seen. Mine has Whitworth in an oval on the top of the front receiver ring but not on the side rail as this one does, nor out on the barrel. I assume the pad was replaced on the one shown here, mine still has its original red Whitworth pad. Only the early ones like this show the Interarms Castle stamp on the barrel as well. IIRC the Whitworth was introduced about 1974.
Whitworth marked actions show up on Mark X rifles too, as do the pads. To my mind these are not Whitworth rifles in the same way that this one is or mine. It appears they had Whitworth actions left over and slapped rifles together using what they had.