Council photos:
(https://i.imgur.com/o6teRLp.jpeg)
(https://i.imgur.com/hZTZoVA.jpeg)
(https://i.imgur.com/5uHmsKn.jpeg)
(https://i.imgur.com/4oMMJ2j.jpeg)
(https://i.imgur.com/M1gDjtz.jpeg)
(https://i.imgur.com/OZ7AoAE.jpeg)
(https://i.imgur.com/diN8IPc.jpeg)
(https://i.imgur.com/4Hit4Xe.jpeg)
(https://i.imgur.com/w1jO3El.jpeg)
This should be fairly simple, as the line is wrong anyway (there should be double-dashed lines there the restriction changes).
Dear London Borough of Southwark,
As the CEO's own photos confirm, there were no visible markings indicating the end of the solo motorcycles bay at this location, a change in restrictions requires a double-dashed line. As no such markings are visible I was entitled to rely on the upright sign indicating solo motorcycle parking, which the CEO has neglected to photograph.
It follows that the alleged contravention did not occur and the penalty charge must be cancelled.
Yours faithfully,
Send this online and keep a screenshot of the confirmation page.
The council will likely reject but I as long as you stick it out to the tribunal, this should be a straightforward win.