It is quite possible that some of these £20 notes were handed over in pure innocence. If they are good quality reproductions it is quite possible that the holder was deceived before handing then over.
If anyone is willing to lend me or give me a useless counterfeit note, I'd quite like to give one a full examination for comparison purposes as I have access to specialised examination equipment. I might then be better placed to provide some advice on detection features using the hand-held equipment I recommended earlier. If so, please drop me a line on:
phil.precambrian@btopenworld.com