jOhn - if you had notified the DLVC (by filling in and sending back the appropriate part of the registration document) when you sold/disposed of the motorbike, you wouldn't still be the registered owner. Presumably then, you wouldn't have received the fine notice.

P.S. If they do find you guilty, drag you down here, and lock you up in The Tower of London, or Wormwood Scrubs, - all the London catters will come and visit you and smuggle files and hacksaws into you - concealed in take-away curry containers.