I have recently had my Leon
cupra windows done with 20% tint all round, its still pretty easy to see in to the car and so i doubt i will have any problems with the police regarding it, the seem to be happy if they can see you and whoever else is in the car.
I say this because for the past 5 years my 4x4 has had 35% on rear and 20% on fronts and i have never been stopped for that.
If you want to be 100% legal you cant touch your front windows and there is no limit to the rears.
But at the end of the day if you drive like a nob or a copper wants to pull you over for a random check they can always use it as an excuse.
I guess its the same priciple as personal number plates if you take the pi** they will tug you for it.
anyway my yellow
cupra looks cool with 20% tints and if i have to buy a couple of front windows from a scrappers to switch them and get my pink slip stamped at an MOT station (if i ever get one) who cares..
good luck..