Pobjoy Mint is based in the UK and was selling the collection predominently in that Country therefore although no hallmarking was required on the coins, it definately would have been on the medal if precious. Silver has been assayed in the UK since the 1500s so it certainly would have been hallmarked. Also it is definately not pewter as it is considered very soft for striking. I work for Pobjoy Mint so I have a pretty good idea that I'm correct and this type of piece was almost certainly a base metal which would have been plated.