Thanks for responding Andy. In short, no he can't he's working away in an area with next to no signal for the next week or so and wants to try and get a head start.
Responding to some of your points:
1. The only charge is s172.
2. I understand the IA creates a rebuttable presumption but can you explain what reason/arguments the Police might give as to why it wasn't received? Simply saying that they didn't receive is not sufficient to overcome the rebuttable presumption. I suppose postal disruptions or strikes might count as rebuttal evidence but have already checked in or around those dates it was posted and nothing occurred.
@NewJudge, you are indeed correct as to the proof of posting. No witnesses were in the car at the time, nor is there any CCTV in the area that he is aware of and even if there was, the alleged offence happed back in September almost 6 months ago. There is a witness statement and it does mention their robust post monitoring system (though it doesn't seem to describe this system except a bit of blurb about how they issue notices) but it reads as if the system is perfect running smoothly 100% of the time. As we all know, things can go missing or get misplaced or otherwise lost so it is not beyond all realms of possibility that processing a substantial number of correspondence, thing could go missing, lost or misplaced. Happens at HMRC, HMCTS and other executive agencies, so why not Northumbria Police?
I appreciate there's an uphill struggle with this one and he now knows if something similar occurs again to ensure it is sent recorded delivery and keep copies of the documents that were sent. As this is outside my area of expertise, if you think the the best course of action is to simply plead guilty then it is what it is and I will let him know.