I still check for them everytime I get a 20p. I check other peoples money too, that's how I got the first one.
I work at Subway, and some guy paid for his sandwich, gave me his money, and I looked at it and noticed the 20p, so I put it in the till and gave him his change, then took the 20p and swapped it with another.
Keep hold of it .. should sell for a good price at one point! The day I found out about it, I search every 20p in my wallet, house, car etc but not one! Iv since forgot about it and realiseing it now, I may of had one =( lol .. im going for another quick searc! =P