I would send the below. I've been out of the loop though so may be missing something on event day challenges. Newham will reject no matter what you say although it's weird that I can find no record anywhere of an event day on 11 August.
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I am challenging the PCN on the grounds that the contravention did not occur and may have been issued in error.
If the PCN was issued owing to the parking place being subject to event day controls, I could find no mention at the location of whether an event day was in operation and no indication by the council of any way to find out.
I am aware that the previous day (10 August) was subject to an event day as West Ham were playing but I can find nothing about 11 August.
My route to Litchfield Avenue was from the Bow roundabout through High Street (A118) to Broadway then briefly to Romford Road, left to Deanery Road to Litchfield Avenue.
I am aware that event days are signed below zone entry signs but it seems that any sign must have been a long way from the parking place on the busy A118 and it would seem to be wholly unreasonable for you to rely on this alone to notify drivers of restrictions in a large zone such that details of dates and zone type are easily seen.
I ask should you reject this challenge to provide evidence of reasonable signage for my case.
Otherwise I look forward to your early cancellation of this PCN.