Yes they can but it also depends on what police force area you are in i had my cars limo black fronts in the 90s and i would say it was not good at night and when there was rain in the dark but in daylight they were fine.To be honest a lot of window tinting companies will not do the front windows or will warn you not to go too dark, mine were done in smoke which is great and offers uvb protection.You under the law can have all the rear windows up to limo black if you want the grey area is the front you can get done at your own risk and windscreen is a no no except for a shade band is allowed.