Just to add my bit as it is my favourite subject.
Roadcraft states there are 5 variations of the thinking distance and another 5 variations for the stopping distance [therefor over 25 variations between drivers and cars]
I have and keep a list of many cars braking distances from 60 mph.
Roughly from memory at the top were mercs Bm's Porsches lexus etc [half highway code!! BRILLIANT]
At the bottom were the old model Dacia [not the new Renno based one] and a Fiat.
Nearly TWICE highway code figures SO if you are in your top of the range motor and being followed by the latter.
THEIR stopping distance includes your car!!
Cheers Andy