Should the location of police speed traps be displayed on signage?

I have been led to believe that police speed traps (of the hand-held variety, not fixed camera) could only be conducted where there was clear signage that a speed camera operation could be conducted. I have just witnessed a camera trap, of the hand-held variety, 200 metres into a 40mph zone from a national speed limit zone. There are no signs anywhere along either stretch of that road to indicate any form of speed camera operation. Also the police had a car situated prior to the trap, I assume, to caution any vehicles travelling away from the trap against signalling oncoming vehicles. Is a headlight flash to vehicles approaching a mobile camera trap illegal?

Asked on 6 July 2013 by PS, via email

Answered by Honest John
Police are not obliged to put up signs any more than to warn that muggers, burglars, arsonists, rapists or murderers in a particular area will be prosecuted. It's simply a matter of good sense to put up warnings where speeding is deemed to be a problem (or a money-maker), so that there is no excuse and that prosecutions go smoothly. It is not illegal to warn approaching drivers of the potential hazard of a speed trap unless the police are able to prove that the approaching vehicles were speeding and that you were therefore assisting them in evading prosecution for committing an offence.
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