I concur that a response as outlined by NajaB would be best. A couple more points:
* Should this end up in court you can have the support of a 'McKenzie Friend' - see the guidelines drawn up by the government
here. Ideally it would be a friend or family member with some familiarity with the law, or if not the law then any professional work that involves presenting evidence, reasoning and analysis (accountant, teacher, lecturer etc).
* Remember that Magistrates Courts will have a Duty Solicitor, who can represent you for free on the day. If the plan were to plead guilty, the duty solicitor may help you to make a case to the magistrates for a lower fine due to your illness.
* Again, should this end up in court, you could try settling on the day - there's a short summary from an earlier case of how you might do this
here.