The video shows you totally bang-to-rights, I can't see anything that might contradict this opinion. Two clear 'No Left Turn' signs with nothing in the way of them to prevent you seeing them.
Of course there may be a fatal error of content in the PCN or the traffic order may be out-of-date. If there is something, you'd inevitably have to take them to London Tribunals for an unbiased decision. This means the discount option wouuld be lost.