Have to look out for you on my travels to Redditch (aunt lives that way)
Its all a legal issue at the mo the tints idea, the front windows (nay the rears too) are already tinted as standard almost to the legal limit (although you wouldn't think so) however you can have the rear sides and rear window tinted as dark as you like but the fronts must only be to 70% light transmission (or some figure like that)