Thinking about it, I think that I enabled this using Carista, although it could be because of TVS software that
@BognorMotors applied.
I have to say that the "Drivability" software that Bognor Motors applied to my van transforms the ACC experience. The rolling back/forwards at slow speed, better gear selection (with lack of clutch slip) were the reasons I had it applied, but when a vehicle overtakes me on a motorway and then pulls in in front of me whilst travelling faster than me, my van saw a lack of gap and slowed! The TVS software sorted that out which was unexpected, but I was pleased as it drove me nuts!
It seems to recognise that a vehicle has pulled in front of me, senses that it is travelling faster and maintains my speed unless the vehicle slows. It is impossible to explain, but transforms ACC in my opinion.