Thanks all for replies. I've had another play with the pistol today (forearmed with the suggestions on here) and, as indicated, the cocking link/shoe is the culprit. So I'm now trying to track a replacement down - The version on the pistol is the first pattern linkage (as per p. 61 of Bruce's book) - Is it possible to get hold of replacements. I see on the various websites (Knibbs etc) that the later version is attainable.

Thanks again for the assistance.

Best

Olly