Regards your case I would seek legal advice from a professional as I suspect if the case for using your phone gets thrown out they might try the "Driving without care and attention", although the fact that you saw them and witnessed them turning round shows you were paying attention
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While driving home a few weeks back I got pulled over (allegedly speeding) and my phone was on the centre console (It was actually on the armrest until the police officer stepped out in the road in front of me at which point it slipped off and landed on centre console), he asked me was I using the phone to which I replied "No, feel free to check the call history and duly handed him the phone", he never even checked it (I guess if he figured I handed it over I had nothing to hide), they did not "do" me for speeding, he said I was doing 43 in a 30 (I was not actually speeding anyway
) as it seemed he was only issuing me with a warning "To slow down" (Still was not speeding officer!), funny thing was tho they pulled me over and not the old guy in front of me who was blatantly speeding (and clearly pulling away from me at the time), I suspect that the radar gun speed they said they had that showed 43 was indeed the old guy in front of me
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