I do have an old analogue Scalextric Pacer system Scalextric Pacer - Run any car as an Analogue Variable Speed Pace car | SlotForum
but it was a bit hit-and-miss! It also had a ten-second program limit. I'm hoping to build a slot car track of my own, for my old classic cars, so don't think I can integrate it. I'm not sure if there's a generic pacer system that can be used with different manufactured slot tracks.
Thanks 
Simon