That makes things very interesting, in a bad way. I had mistakenly believed by reading your initial post that you had passed a police officer (which wasn't the case). The good news is, careless driving is one of the hardest HTA charges to prove, so the Crown has an uphill battle. Just out of curiosity, how did you become aware of the fact that a person with "power" status was the one who made the complaint? Did the police tell you?
Also, did this person-of-status manage to positively identify you when the alleged incident happen, other than just note your licence plate? (I know... sounds stupid... but...) If he could not get a clear look at who was driving the vehicle and be able to identify you later, their chances of a conviction are almost nil. This is an offence where they must identify the driver. They will require this person to attend court for a conviction, at which point he'll get embarrassed on the witness stand. Getting a paralegal involved would be worth every penny, IMHO. The whole scenario reeks of abuse-of-power.
In the mean time, put together some concise notes on exactly what happened, the weather, road conditions, vehicles involved, scenario, etc. If this person "aggressively chased you," that is not so much "careless driving" on his part, but it falls rather nicely under section 172. 