Plenty of unmarked cars on the A23 between Brighton and Gatwick. Always tend to be silver, seen an A4, Merc C class, BMW 3 series, Octavia RS, even an Evo.
The guys in the Evo were naughty boys, I was in my 200SX, they came right up behind me and sat on my bumper in what I can only imagine was an attempt to get me to floor it. As far as I know this kind of tactic is not allowed by the police (?!).
Only two problems with their plan;
1: I'd seen a silver Evo pull someone over a few days before....
2: My 200 is standard which I know is no match for an Evo so I was never even going to attempt to 'race' them....
Be careful folks