We've seen this one before. I expect your driver approached the junction on Prince of Wales Road, wanting to turn right onto Shooters Hill Road, but right turns are barred, see GSV: -
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So your driver drove on into Stratheden Road and turned right at the again barred right turn show on your photo hoping to get away with it. You can look at the video of this if you ring-up TfL and ask for it quoting the PCN number. TfL are, sadly, in the IT Dark Ages now, because the video is sent as a DVD. The PCN enforcement process will be frozen for about 10 days to give them time to produced it and send it out. Quite why TfL have this rather stupid system instead of having the vidoes on line like the London councils, only TfL know.
Anyway, I don't think you'd get much joy at London Tribunals, (TfL will obviously reject your reps), because the No Right Turn signs are clear enough. HOwever, there may be a technical appeal suggested which is unrelated to the contravention itself, based on TfL mismanagement of the enforcement process, so wait a bit to see if anything is suggested.