Don't get caught out with the old £20 pound notes...
Businesses will no longer take the old £20 pound note as of the 30th June 2010. Below is images of the old ones and the newer versions.
New and current ones have the image of Adam Smith on them (top one of below image)
Old ones that's best not to get caught with after 30th June have an image of Edward Elgar on them (bottom one of the below image)
Best thing to do is take any old ones into the bank and they will change them for you. I did mine this week, but don't know what happens after the 30th June...