The law is a bit tricky when it comes to window tinting so lets look at the bit that is perfectly clear. All windows from the middle of the car (from the B-pillar) backwards CAN be tinted to any desired level.
The front windows (windscreen and and door windows) can be tinted, although not by much. Some people will say that the front windows can not be tinted at all, whereas others think anything upto 30% (allows 70% of light through) is legal.
To be on the safe side we recommend the following guidelines:
In the majority of cases you will be issued with a delayed prohibition which states the tints must be removed within 10 days. However, in some situations where the tints are too dark (less than 30% of light gets through) the vehicle can not be moved under its own power until the tints are removed.