Ok if I understand correctly, you have received a FPN, up to �1000, for no lead (crime B), but the letter states that it is being passed to the legal dept because you did not pay the previous FPN, up to �2500, for fouling (crime A).
You would have been sent a FPN for the first one, and they will take you to court for not paying it. I assume you are saying you never received it so this should be your defence (how can you pay a fine you didn't receive). The downside to that though is that there would have been at least one or two more warning letters sent to you before getting to this stage which you obviously didn't respond to either.
Is there an initial lower fine for both offences if paid within a certain time? If so contact the council and ask if they are willing to accept those payments to stop it going to court.