I remember reading a story on teletext once in, presumably, 2003 or something, that in the 20 years since the pound coin had been released, 800 million of them had gone missing.
So I decided then that I would collect all the missing ones, and that would be how I made my fortune, and ever since I have dedicated my entire life to finding them.
So far I have found 4 pound coins.
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Notes:
1. Written on August 13th, 2016
2. Unfortunately now my quest has been ruined by the introduction of a new pound coin
3. I shall never forgive them