Basically, their right, legally, you can't tint the windows in front of the b pillar any more. DOn't listen to the people that bang on abot '35%' being legal.... I had a specialist company tint my windows, and when the law changed they asked me to return to have it removed. Even though it was a 'ultra light' tint. The reason for this is that all car windows are tinted by the manufacturer anyway, usually at about 17-20%. This is built into the glass. Adding even the light tint puts it to beyond 35%, so legally your stuffed. Reputable tinter wont tint front passenger windows, but plenty of people are still getting it done.
The problem stems from the tossers that think its cool to have completly blacked out windows.... a few accidents have been attributed to tinted windows, even at least one death. The governemnt jumped on this, despite the fact that most adults over the age of 50 that don't wear glasses can't see past the end of their noses....
I didn't have my tints removed. So perhaps legally I'm in a funny spot. But then again, I know I have perfect eyesight (laser corrected vision) and I'm a 'very careful driver' (ask anyone... never break the limit).
It will be interesting to find out what the position is when I get my car MOT'd for the first time next year....
The police in my area really don't give a stuff about tinting.... seems the same in most of the South/London area. I have heard of areas where they enforce it though. At the end of the day, I'm middle aged and sensible (for the most), I think if your a kid and go to cruises, and have one of those uiterly pointless 'Big Woofer' sound systems, you might get plods attention.