UK Law states that your front windscreen must let through 75% of light, and your front side glass must let through 70% of light. As pretty much all cars produced today have a slight tint in the glass from the factory, if you choose to have your front glass tinted you could be breaking the law by using your car on a public highway. For more details on this please visit the VOSA website.
Legally, you are allowed to tint all glass behind the driver (B pillar backwards) as dark as you choose.
Having tinted glass may also affect your insurance policy
Top Tints will not take any responsibility should you choose to take your car on a public highway should you decide to have your front glass tinted. It should only really be done for show / track use only.