unmarked 330d 5 series Bmw dark blue M4 between junction 17 chippenham and 18 bath westbound, returning to go back east bound, probabley from swindon area.
I got pulled by an unmarked 330d round about there last year on the way to Le Mans - at about 2am doing around 95 on the bike... he ticketed me for my small plate but let me off for the speeding.