The photographic evidence does not showing us prior to or passing under the gantry. That evidence they have in their possesion - it is a full defence to this.
How do you know what they have?
The photographs you’ve posted here are the standard set for those detected speeding by HADEC3 systems: two photographs of the vehicle after it had passed the gantry and one taken almost simultaneously of the gantry display (to show the limit that was displayed). There is sometimes a fourth showing close-up of the vehicle for identification.
Why would they have – or require – photographs of your vehicle prior to you passing the gantry? The offence is only committed when you pass the speed limit sign.
From what you have shown us, the offence seems complete. What you will be suggesting to the court is that the gantry display changed between the time you passed under it (when you claim it was showing “50”) and the time your vehicle was snapped and a photograph of the gantry display was taken simultaneously, probably about a second later. On top of that you will be arguing that (a) the delay in enforcement of at least ten seconds (I think the delay is actually a minimum of 60 seconds, but no matter) after a change of limit failed and (b) that the system showing that the lower limit had been imposed for more than an hour prior to your arrival was also faulty.
If your contention about the "manual override" of the system overcoming these constraints is sound you will need to get some evidence of that. I don't know whether such a difference in operation exists but my instinct would suggest to me that it does not.
What you are asking for on here is concurrence with your line of defence. Going on what you have shown us I cannot concur and I doubt the court will unless you come up with some other evidence to show that the system had failed - or had been overridden as you describe.
If you do find out that anything was amiss with the system do let us know. I, for one, am intrigued.
