Makeitfit, personally I wouldnt bother trying to tint the front windows because there is legislation preventing this.
The law states that any tint must allow at least 70% of the light to pass through them - most vehicles come with a degree of tint already in the glass, and are normally close to this mark anyway - adding any amount of tint - even 'lightsmoke' is likley to make them illegal!
VOSA has spent £13,000 providing light meters for roadside checks. If the meter detects between 45% and 65% of light getting through then you would be asked to remove the tint, failing to do so could result in a £2000 fine. If the meter says 30% to 45% the vehicle is deemed unfit for the road and a delayed prohibition is issued leaving 10 days to remove the tint (the police will normally make you remove a section of tint at the roadside - cause once it looks naf you'll want it all of anyway!). Less than 30% and the vehicle cannot be moved until the tint is removed - which generally involves ripping the whole tint of at the roadside.
What is excessively tinted glass?
Motor Vehicles first used on or after 1 April 1985:
The light transmitted through the windscreen must be at least 75%.
The front side windows must allow at least 70% of light to be transmitted through them.
If the glass is tinted to a point whereby it lets through less light, then the vehicle does not meet legal requirements - and may also invalidate your insurance with this modification, particularly as the vehicle is likely to be illegal.
Trust me.... I speak from the experiance of my 'boy racer' days! :augie
I like your back windows though... mine have the factory tint on already - but I wish it was darker!