For a long time one of my Felicia keys has not worked, but now the other one has stopped working as well. I think the problem may be related to the Immobiliser Control Unit as everything else seems fine. Unfortunately I do not have the original tag with the ignition key code. Any suggestions as to how I might deal with this problem or do I need to see a dealer?

It's officially a dealer job, but you may be able to find a specialist who has software that can get the code from the immobiliser box. The problem could also be another part of the system such as the read coil around the ignition switch, or it may not be immobiliser related at all.