That's not how red lights work, at least not in the UK. The rule is that you cannot cross the stop line, your stop line would have been here:
(https://i.imgur.com/NMniONZ.png)
Once you're past the stop line, the lights simply don't apply to you and you're entitled to keep going. This means that if you're halfway across a junction when the lights turn red, you can (and usually should) simply keep going.
So while I appreciate why you stopped where you did, the law on red lights did not require you to do so.
As for the PCN, here's a simple representation you can send, I recommend you put this into a PDF document and upload it to the council website as an attachment, together with a photo from your car's owner's manual showing the length of the vehicle.
Dear London Borough of Waltham Forest,
I challenge liability for PCN FR60117364 on the grounds that the alleged contravention did not occur. As the video confirms, there was space ahead of my vehicle when I stopped:
(https://i.imgur.com/wqjFI02.png)
I could have proceeded further, but chose not to do so because I would have then obstructed the pedestrian crossing. My path was not blocked by stationary vehicles.
My car is 14.71 feet in length, and having measured the gap in front of my car using google maps, I can see there were at least 14.34 feet clear ahead of me when measured perpendicularly to Lea Bridge Road:
(https://i.imgur.com/PkJACuT.png)
As I was travelling at an angle, there was actually ample space to accommodate my vehicle without colliding with the car ahead:
(https://i.imgur.com/tz88try.png)
It follows that I did not stop in the box junction because my path was impeded by stationary vehicles, rather I stopped because I chose not to obstruct the pedestrian crossing. It is a common myth perpetuated by councils that stopping in a box junction for any reason is a contravention, but this is not the case: it is only a contravention if the vehicle stops because it cannot proceed owing to the presence of stationary vehicles. Where a vehicle stops for some other reason, whatever that reason might be, the contravention alleged cannot occur.
It follows that the PCN must be cancelled.
Yours faithfully,