Followup on the speeding allegation

The advice I've seen from PePiPoo and Richard Bentley and the Association of British Drivers is this:

I have an absolute defense under section 84 (4) of the Road Traffic act of 1984. (Which sounds good, I'm not 100% sure what it means, but as best I can tell, a legal speed restriction absolutely must comply with signing requirements).

Basically, in order to apply a Endorsable fixed penalty notice (EFPN) using the letter of the law, they also have to comply with the letter of the law. As such, no offence was committed.

I've still not sent back the Notice of Intended Prosecution (NIP). I am intending to do so with a covering letter, explaining the situation. Before I do that though, I've evidence to gather.

Does anyone feel like a short drive through the countryside before the end of the month, and is prepared (if necessary) to act as a witness? Could probably do with taking some video footage of the route too, which is ok, as my phone can (albeit not at very high resolution).

The only minor difficulty being that there's multiple routes through this restriction, and on one of them the signage is correct. So I then have to figure out the situation as regards the burden of proof.