Had a similar incident only it was two off duty rookies in a private vehicle. They drove past me waving badges, I ignored them and carried on to my destination. As they followed me into a parking area I called 911 claiming a possible car jacking. A marked car arrived immediately and the two guys following me were immediately hand cuffed and placed in the cruiser. The attending constables confirmed that the two were indeed policemen and that they were claiming that I had been driving over the speed limit.
I replied to the attending constables that if I had in fact been speeding so had the off duty constables and in a vehicle likely not certified to give chase. The attending constables returned to the off duty constables and after a brief chat returned to their respective vehicles and drove off without so much as a goodbye or a wave.