Here's an initial draft:
Dear London Borough of Redbridge,
I challenge liability on the basis of a procedural impropriety. The location of the alleged contravention is given as "High Road", the PCN mentions bus stop A which I have not been able to locate but there are no less than 33 bus stops along this road.
I was not driving the car at the time and in the circumstances, the PCN fails to adequately particularise the location of the alleged wrongdoing.
In the circumstances the penalty charge must be cancelled.
Yours faithfully,
Send it online and keep a screenshot of the confirmation page.
In the meantime I'll get the data about the make and model of the camera.