Yeah, they do that.
Here you are allowed 75% vlt on the fronts which is almost what the factory tint on the glass has so my super light 75% vlt additional tint will put it over but won't be silly dark.i think front side windows max tint is 75% VLT (or whatever the acronym it's supposed to be), rear glasses are 35%.
when i take it for annual inspection, i keep the front windows all the way down, lol.
In the UK the laws argument is for safety but i think being able to see inside the car has something to do with it too.I've never had tinted car so didn't know any better but 35% all around seems perfect to me. It looks quite dark from outside and hard to see thru, but from inside, it's perfect. And it looks far nicer with all glasses (minus windshield) - split VLT for front and rear side glasses detracts from asthetics, methinks.
Although, I was in someone's car as a passenger with very very dark tint all around at night once and that was rather claustrophobic.
I don't know if VLT limit is for safety purpose or police surveilence purpose (some random told me this). For my next car, I'll definitely get it tinted as well and maybe experiement with different VLT.