Forgot to post this after it was written. Don't know if adds anything. @Greg Heinrich The reason I believe the coin MAY NOT be genuine is the quality of the surface and all the imperfections. I've examined aver a dozen of these in the past and have NEVER seen one this "crude." None of them were counterfeits SO THAT's the ONLY reason I can think of why the one you posted MAY be OK.
Yes, the coin is more worn than usual for the type. But there is evidence that Cromwell's coins circulated, despite being intended as patterns, so the wear in itself doesn't make me suspicious. The style, weight, size are correct. There's no sign of casting. Is there anything that arouses suspicion about a transfer die forgery? That's the only remaining question I have.
No signs of casting? I'm not saying the coin is a cast but it certainly looks like a cast. Pull up a magnified genuine example on the Internet and compare the coins. IMO, the coin is not "mint quality" and we'll never know if it is genuine until it is slabbed and someone sells it on the net. I'll remember that one in all my nightmares.
I'm NOT insisting on slabbing - I hate the things! It needs to be authenticated. If you have access to an internationally regarded English expert - go for it! That's a great coin for a blind man's collection. He cannot ruin it!