Remember that (excluding pre-decimal) there is no such thing as an obsolete Victoria chip. Old chips are still turned in more frequently than you would think. When I got the 20p last year (actually I had two of them) I also had about half a dozen 25p's and maybe 10 of the 50p's.

These had all been turned in during a 6 month period. I picked up about 100 chips not in current use all at one time.