Unless a notice of intended prosecution was served at the time, a
Summons can only be issued within 6 months of the alleged offence.

You need to find out which Court they are using, and make a statutory
declaration in Court that this is the first you have heard of the
matter.

This will be the best course of action, even if without you knowing
about it, the authority managed to prove the case in your absence,
since your declaration, if accepted, will nullify the proceedings to
date, and (if they wish) they can start the process all over again, but
at least you will know about it this time, and be able to defend the
case.

Quite apart from this, the Limitation Act prohibits any debt action
after 3 years, so they are likely to be statute-barred now in any
event!

Marc.