I've been caught by one of those, but they're not legally enforceable. Shitting meself I was for 10 days, waiting for the NIP and the prospect of an 8 hour waste of time in a classroom lectured by a patronising twat who seriously believes going 35 in 30 area will kill but 34 won't, and then all I got was a police-letterheaded warning. "GREAT NEWS!".