I can't say with any certainty that its not a garage job, but I would certainly lean that way. The weight of this coin is 7.9 - 8.3 grams. They were made at two different mints.
The Royal Mint pressed them with Medallic alignment. The Heaton Mint pressed them with Coinage alignment. The two holes look like some one was trying to make a button.Your coin is completely missing the other side, I don't see ANY traces of it. It may be a vise job. Draw your own conclusions.