Silver 1 Penny. British Coin.

It looks plated to me. Could you get an accurate mass?

what does it weigh?

HH

By far the most probable explanation for such coins is that it has been privately plated after it left the mint. I own an Australian "silver" 2 cent coin - also originally bronze and about the same size as a British 1p - which my father made as part of an electrochemistry demonstration many years ago. It has been electroplated with zinc.

While it is theoretically possible that it is a "wrong planchet mint error", the chances of this occurring are very small. Wrong planchets are almost always the wrong size - they are off-centre, wrongly shaped and/or have bits missing from around the edges. A wrong planchet that was bigger than the original coin is supposed to be tends to splatter everywhere when struck, and a wrong planchet that just happened to be exactly the correct size would be an extremely odd coincidence.

Wrong planchets also usually get pulled out of circulation rather quickly, since they will clearly not resemble any correct coin in circulation at that time. Your coin has seen considerable circulation; this means that it is surely a plated coin and that it was not a mint-fresh coin when it was plated.

I should also point out that, in Britain, it is technically illegal to plate a copper coin to make it look silvery, since it can now be more easily confused with a higher-denomination coin.