For my tuppence worth:
I got 'flashed' this time last year.
They say they sent me a NIP whcih I never got at the time.
7 weeks after the 'offence' they sent me a letter chasing the reply I hadn't made.
Cutting to the quick...
At court, I produced my wife's original NIP (because I named her as a POSSIBLE driver at the time) and compared their copy - they both had a signature.
Once this had been accepted by the persecution, I pointed out the missing signature from their copy of the NIP they had said they sent me in April; I asked whether it was okay for them to break / ignore the requirements of the law on their side to convict me.
The magistrates agreed with me and threw out both failing to name the driver (where I had given an either or [me or the wife], but saying it was probably me), and the speeding charge - solely, so he explained (the chairman of the Mags) because the ticket office 'had not followed procedure' and they could not be sure whether the original, missing NIP had been signed or not...
Read the thread here:
http://forums.pepipoo.com/index.php?showtopic=9425. And look at the scanned copies of the NIPs produced in court.
Good luck