No, the dovetailed steel plate is original, not a remedy for a later problem. This was a common feature on hammer rifles from this period, especially those from Webley & Scott, which I think this gun may be from. Holland sold a lot of P. Webley & Son, W & C Scott & Son, and later Webley & Scott products under their own name. Excepting the hammer safeties and the engraving, this gun is a ringer for the Webley 435 H. C. (Hammer Cordite) illustrated in their 1914 & 1922 catalogues. Included in the catalogue description - "steel plate across face of action". I've seen quite a few of these with the dovetailed steel plate exactly as in the photo.