£50 note Watch
If you don't want to go shopping with it, I am sure the post office will change it up.
failing that banks, the post office etc. will usually change it for you although some retailers demand you buy something before changing it.
I figure if that special hologram works (i.e it moves about), it can't be fake...
That and the colours are meant to rub off, but I generally don't test that.
As long as any note doesn't feel funny, and looks well printed, I accept them.
We count many thousands in one go, so you can't be testing every 20-50 you see in a forensic way.