In fact I had already sent in my representation when I read your last post,
@cp8759, and this was the representation I made:-

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I have today received the notice of rejection.
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This is my summary of their responses to the three points in the representation.
1) The contravention did not occur
- they say it did because a traffic cone is enough.
2) Procedural impropriety (A regulation 9 PCN must include wording that representations "must be made to the enforcement authority in the form and manner and at the time specified in the notice to owner.")
- This confused them, I think, and me.
An additional piece of maybe relevant information is that before they had sent the NTO I had (foolishly) submitted a 2nd informal representation with points 1 and 2 in. They replied at that point (21 Feb) to say 'a further attempt at an informal challenge is not possible', and 'The second challenge you submitted will be held on file until you have submitted your formal representation'.
They seemed to think I was complaining about them not considering my 2nd informal representation - but of course I wasn't.
3) Procedural impropriety (28 day period wrong) - they kinda disagree.