Before ...
and after.
I didn't know, but the Bank of England apparently issued new 20-pound notes in 2007 and announced that old 20-pound notes wouldn't be in use anymore after June 2010. What?! It's July 2010 already! Kind of in panic (because I brought old 20-pound notes and keep more old 20-pound notes in Japan), I went to a branch of NatWest to exchange my old 20-pound notes for new ones. An unsympathetic clerk told me that I have to ask my bank to exchange. Geez, I don't have a bank account in the U.K. Well, actually, I keep it with NatWest, but I don't have my cash card or account information with me this time, ahhhhhh! In addition, the clerk coldly said that shops in town will not accept old 20-pound notes soon (they currently do now). What the hell should I do with these old notes?!
At a loss for what to do, I went to Cardiff Bay anyway while the weather was good. There, I found another branch of NatWest. To take a chance, I went into the branch. A-ha! I was lucky. A clerk there was such a nice girl that she exchanged all my old 20-pound notes for new ones (I still have old notes at home though)!
Then, I remember that different people say different things in the U.K. It is worth trying things a few times, and at the end, everything will be all right. That is the British way.
Incidentally, according to the website of the Bank of England, the Bank of England will exchange them indefinitely. Phew.