"do I have any grounds to appeal this one?"
You may well have, but we cannot possibly tell unless we see the video, their sole evidence of the alleged contravention. This being TfL, (who are not just in the Dark Ages, but well before them IT-wise !), they only show these on request by you requesting the video and them sending you a DVD by post.
So please ring them up, quoting the PCN number and request the DVD. They will put the PCN on hold for 2 weeks and send you the DVD. DO be very well aware that when the 2 weeks is up, they will reopen the enforcement process. So once you've had a TfL committment to supply a DVD, put the end of 2 weeks in your diary/calendar, because shortly before you need to contact them again if the DVD hasn't turned up.
HOwever, assuming all goes well, please post the video on here for us to look at. A number of conditions have to be met before the alleged contravention is actually made out.
