Free Traffic Legal Advice

Been charged for using a mobile phone and driving through red lights.

true story, I was driving through a serious RTC with a car overturned and full of police and ambulance crew on a junction. Manor House in north London.
I had passenger in my car at the back and was showing him the scene and pointing towards the right side of carriageway just at junction. As approached the junction a police officer stationed ahead signalled me to drive forward as the junction was getting clogged up. I listened to his order and did not take note of the traffic light being red which I have no recollection of the colour.
A few days latter i receive a NOIP from an officer that claims that i was using a phone to record the scene and that i drove through the red light. He claims he gave chase to my car and that i sped off which if he thinks i sped off and feels i made a mockery of him, which i think its the reason he went against me now and says that i was using a phone and went through red light.
i intend to plead not guilty but want to hear advise from here. or should i take a solicitor?

Thanks for pre-emptively telling us that it is a true story. Saves wasting time assuming that you made it up.

However, if you had gone to the trouble of making something up, at least presumably the story would have contained some relevant details (albeit that they would have been untrue).

Where were you in relation to this traffic light when the occifer instructed you to move along?
I note that you do not explicitly deny using a phone.