My mates screen on his Golf is too dark and thats standard fit. Sickening really, but he's been told by the police he must change it, but there is the safety issue with some front tints you can't see a thing. We put ours on due to my sons problem with too much sunlight as he used to pull the blinds off.
http://www.totalcartint.co.uk/legal.htm info on the legal side