You can find the Moran decision here
https://www.ftla.uk/the-flame-pit/dart-charge-pcn-flaws/msg27921/#msg27921It is, so far, untested against a CAZ case. Bristol have shown substantial reluctance in letting a case get to tribunal where this argument has been raised.
Will it work for CAZ? It ought to, it's the same legislation. But there are other considerations.
- In Moran an underlying charge had been paid. An adjudicator may consider that in some way.
- The authority have, in effect, agreed to drop the penalty in exchange for the CAZ fee. Might this hold some sway with an adjudicator.
- If you win, are the authority still entitled to attempt to enforce the CAZ payment being due (I guess they'd have to ask you nicely and eventually sue you if they felt they really wanted to collect). I don't see any regulation which would discharge the letter ability. Though it might.
An adjudicator is not bound by another adjudicators decisions. Even one made by the Chief Adjudicator.
It is a strange state of affairs that the charging order for a CAZ can legitimately demand the toll, however the underlying regulations give no means of enforcement.
Not all charging schemes do allow the fee and a penalty (Birmingham don't, TFL don't for example). I think it may be the case that these were better advised.
(This also leads to another oddity. If the scheme does not apply the charge in addition and exceeds the penalty charge then why pay at all. Just settle discounted penalties).
I would like to see a CAZ case on this point, but you do need to consider what may be gained either way.