I'm seeing a considerable degree of wear. If it were a genuine "mint error", i.e. a penny struck on a halfpenny planchet, I can't understand how it could have acquired that much wear from circulation. It looks so odd and different from a normal penny or halfpenny, someone would have put it aside, or a bank spotted it and withdrawn it.
So I'm guessing that it was once a perfectly normal penny, that someone has (for whatever reason) decided to grind down to a smaller size. Maybe they wanted a nice portrait of George V to insert in the head of their souvenir teaspoon, or something. Or it may have come from a piece of "trench-art" (bored soldiers making souvenirs from coins).
Quote:
Is there a date on it?
The date would have been beneath the exergue line on the reverse. The entire exergue line is missing from this piece, so it's impossible to give it a date.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis