Informing oncoming motorists of speedtraps

Question

I was hoping that Arrive Alive could provide some advice: a friend of mine and I have been trying to decide whether it is technically legal to warn someone of a roadblock or speed camera, but we can't seem to find anything on the internet to answer our question. Is there any legislation/regulation/case law prohibiting such behaviour, and particularly flashing oncoming traffic to warn them?

Answer

The question is whether this would constitute "Obstructing the course of justice"? There has been reported case law on this! -and the problem for traffic authorities is more one of proof of the offence and intention. The prosecuting authorities would have to prove intention on your part - which constitutes "Will" and "Knowledge of Unlawfulness". This means in practical terms that they would have to prove that you have known that the oncoming traffic has been exceeding the legal speed limit and that you warned them whilst having this knowledge... a near impossible task.... It gets people to slow down, doesn't it..????