In any box of After Eight Mints, there is always a large number of empty envelopes and no more that four or five actual mints. The cannock chase is the process by which, no matter which part of the box often, you will always extract most of the empty sachets before pinning down an actual mint, or 'cannock'. The cannock chase also occurs with people who put their dead matches back in the matchbox, and then embarrass themselves at parties trying to light cigarettes with tree quarters of an inch of charcoal. The term is also used to describe futile attempts to pursue unscrupulous advertising agencies who nick your ideas to sell chocolates with.
|source : The Meaning of Liff|