If the car is stationary, then there's no driving involved, hence no fine. The copper sounds like a right ***, as do the others that agree with him. HE WAS NOT DRIVING HE WAS STATIONARY.
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The law doesn't care, if you are in traffic you are classed as driving, for all the police know someone waiting at traffic lights could have been on the phone for the past 5 minutes, and planning on being on it when the lights change.
It's harsh, but the chances are most people who are seen using mobile phones at the lights are likely to continue using the phone when the lights change.