Wow, we haven't seen this sort of thing for a long time !
It's an Excess Charge Notice, (ECN), and comes under the regulations they cite on the ECN. Best if you go to their suggested website to see what the score is, but normally these things are under the criminal law, not the civil law, but my knowledge of these peculiar regulations is almost non-existent, However, I do wonder at the reference to a "Notice to Owner" on the ECN, because this is a specific statutory document within the de-criminalised legislation for traffic and parking contraventions only.
Anyway, I have had a quick look through the regulations, (what a pain !!), and nowhere in any of them is any reference made to "Notice to Owner". There is nothing at all about submitting representations or any formal structure for their receipt and assessment. So my conclusion is that enforcement is a matter for the magistrates courts but I may be wrong on this, so wait until others have contributed.