There is no informal challenge for moving traffic contraventions, you get one chance to make representations and then it's off to the tribunal.
Here's a draft:
Dear London Borough of Newham,
I would like to request cancellation of PCN PN74598545 for the following reasons.
I am well aware of the Healthy School Streets scheme and my child has a disabled access permit for Dersingham Avenue
I have uploaded the following three diagrams I have drawn and would like you to consider:
Diagram A shows my normal route for drop off to school: LINK1
Diagram B shows my route on the day of diversion, when approaching Dersingham Avenue there was signage indicating a road closure so I drove further up to do a u-turn and when retracing my route, on nearside there was a diversion sign directing traffic into Sheringham Avenue: LINK2
Diagram C at LINK3 shows my route on the day of the alleged contravention, owing to the position of the signs on the previous day I did not become aware of the fact that the diversion signs had been removed until I had already committed to the turn and because Sheringham Avenue is subject to a one-way restriction, it was not possible for me to return to Romford Road. Having seen diversions signs because of road works on other parts of Romford Road and heavier traffic than normal I had understood that the diversion was still in place, and I did not want to drive further up Romford Road and do a u-turn for a second time given that I was already delayed in getting my child, which in itself was problematic owing to his special needs.
I have since applied for a permit to allow me to use Sheringham Avenue which has been granted, I have uploaded a copy at LINK4
I trust that in light of the above you will be able to cancel the penalty charge on this occasion.
Yours faithfully,
I will PM you the links to put in the representation,if you give them the links I'll PM you, we can use the click count to confirm whether they've looked at them or not (obviously do not click on the links I PM you as we want the click count to remain at zero). If they don't click on them, we can then prove they've failed to consider all of the evidence. If they say in the rejection that they've considered all the evidence, we've got them for lying as well.