Not worth the hassle. I got pulled on the motorway in Manchester a few years ago. They tested my front windows and they were found to be illegal.
They phoned for a recovery truck to take me to a compound.
I then had to remove the film, take the car to an MOT station to get it verified that it was legal, then go back to the Police station and hand in the certificate.
Or at least I would have if a "shout" for an armed robbery hadn't come in and they had to rush off. I was informed in no uncertain terms that I was vey lucky, they cancelled the tow truck and let me go on my own recognisance.
I removed the film when I got home needless to say!