WHAT IS THE PURPOSE OF THE LAW
The purpose of the law is to ensure the driver’s ability to see the road is not excessively restricted by tinted glass.

WHY ARE TINTED WINDOWS NOT PART OF AN MOT
Tinted glass is seen as a serious issue, but only affects a small number of vehicles.  To include this item in an MOT test would require all MOT stations to purchase special test equipment.  With only a small number of offending vehicles a roadside enforcement is a better route as it targets the offenders, while minimising the cost and inconvenience to compliant road users.