Interestingly, I've just had a look on Havering's own website and it links to their policy on Enforcement and Cancellation of PCNs.
There's a link here -
https://www.havering.gov.uk/downloads/file/96/policy-for-enforcing-or-cancelling-a-pcnIf you scroll to the bottom, you will see Appendix A, where you can see that it lays out an application to the London Councils Transport and Environment Committee. It is dated 2013, but has not been updated or confirmed as to whether or not the application was agreed either way look at Point 8, and then Point 15.
I would argue (and in fact shall be arguing as one of the points in my defence of this PCN) that where this PCN states - "We cannot accept verbal challenges in person or on the telephone." which is in bold on the PCN, that this fetters discretion and is in direct contradiction to the council's published policy. That the statement is in bold is, in my view, important as it suggest that this is an absolute. I think that because the PCN says something that is in direct contradiction to the council's own published policy of enforcement/cancellation of PCNs that it is automatically unenforceable.
I would appreciate the thoughts of others on this matter.