law is, you can do what the hell you like with any of the glass behind the Bpillar, you can grab a brush and paint them with black hammerite if you do so wish.
Law on the front windows is that they MUST let 70% of light through,
but before you go booking tints, remember that if the glass has 43R stamped in the corner, it means it already carries a factory tint of around 20%!!
so basically, its illegal to put ANY tint on the front window!!
i know people who have put the lightest of tints on the front window, and been stopped and checked, and the police machine measured only 30% of light getting through!!
so the easiest thing is....DONT TINT THE FRONT!
and the best thing to do is NOT TINT ANY! because it looks horrible and chavy!