Here's my draft submission. Please advise if you think of any other grounds. Thanks
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I entered the box from the right lane at 15:28:40, confident that the way ahead was clear, As I began to move to the left lane I had a sight line of the left lane flowing easily around the corner ahead, where the A3 rounds a bend and leaves the South Circular to continue straight. No sooner had I moved into the left lane than a car in the right lane ahead of me made a sudden lane switch, perhaps upon realising they were in the wrong lane. The sudden move caused the security truck ahead of me to perform an emergency stop to avoid an accident. The after-effects of the emergency stop can be seen in the video as it causes the security truck to rock back and forth several times, following its suspension being heavily compressed during sudden hard braking. The car behind this truck was also forced to make a sudden stop, as was I, causing me to become briefly stuck, halfway inside the left side of the box.
When entering the box, I very reasonably anticipated my exit ahead would be clear. Reasonable anticipation of the behaviour of other road users is a fundamental pillar of safe motoring, a lesson drummed into every learner driver, yet we all know that no matter how carefully one drives, and however reasonably one anticipates the behaviour of other road users, there is always a risk that another road user will do something sudden, dangerous and entirely unexpected, with little or no regard for their fellow road users.
I contend that there was no contravention, as when I entered the box I had every reason to expect my exit from the box to be clear of any obstacle. I cannot be held responsible for the behaviour of other road users.
I further contend that the contravention alleged in the PCN could not have occurred at the time alleged in the PCN. According to the time-stamped video evidence captured by TFL, I was leaving the box at 15:29, not entering it, as the PCN alleges.