Cheers Chris
But I agree with your argument that as I haven't been stopped I have no way of knowing of an intended prosecution (other than the fact that I went past the van).
They have 14 days to send the NIP to who they reasonably suspect is the registered keeper (or some legal gubbins) - which is me at my home address because they manage to send my tax renewal here every 6 months.
I think they then have 6 months to start a prosecution if they want (statute of limitations?).
I'm betting it comes through the post tomorrow now, but I'm still going to keep hoping.