I just noticed your post, I don’t know that much about pcns, however a family member of mine was diverted into the CC, and I managed to get TfL to cancel it or they eventually chose not to contest. I think they knew id take it to tribunals given the substantive reps I had sent to them. I recall including diagrams of the diversion and quoting the following in my reps, as they may have failed to consider: S14(3) of the road traffic regulation act 1984 which requires that: “when considering the making of an order or the issue of a notice under the foregoing provisions an authority shall have regard to the existence of alternative routes suitable for the traffic which will be affected by the order or notice." I may have additionally cited chapter 8 (part 3) of the traffic signs manual (2020) point u2.19.3. which recommends that: ”for motorised road users the requirement is that the diversion route shall not have any extra restrictions (including weight, height, width, emissions, or vehicle type) or pass through any additional tolls or charge zone.” Please note TSM is only guidance. Interestingly, similar to another local authority, they also failed to process my formal request for the traffic camera footage nearby the diversion, I either made an FOI or EIR. Your case slightly different to mine, as you mention the diversion was implemented by another authority, however its possible the same principles may still apply, however I cannot be certain as I’m just a layman commenter, perhaps wait for a response from other experts with more knowledge or alternatively seek advice from a legal practitioner in traffic law. Nonetheless, thought id provide an insight into my experience, also I managed to get TfL to cancel a separate CC pcn but for another legitimate reason altogether, therefore don't lose hope. Wish I could help more but unfortunately my health is deteriorating quite badly, so this response is all I can manage.
