Answers on a postcard please

Further to yesterday's post, the question which immediately springs to mind is why did the CPS decide to prosecute?  The CPS have to consider two things - firstly, is there a realistic chance of the prosecution succeeding?  This is usually taken to mean a better than 50-50 chance.  Here there would be no problem - there was after all decided case law going back a hundred years or so.  But secondly, they have to be satisfied that prosecution is in the public interest, and here It would be interesting to know their reasoning.  Back in 2001 the Ministry of Transport published guidelines for the use of speed cameras - specifically they said that such cameras should be easily visible from a reasonable distance, painted yellow and no longer hidden behind bushes and such.  The reason for this, as stated by the Ministry, was to give the motorist the opportunity to regulate their speed before passing the camera.  So what was this man who was fined doing other than precisely that?  In which case how could it possibly be seen as in the public interest to spend significant amounts of public money and take up significant police time in prosecuting him?  Anybody from the CPS prepared to comment?