Not sure, as I want the car to be FIA legal I need to opt for a more expensive option for the front screen than say would be needed for a drag race car. Construction and use regs, or whatever the headed papers been changed to this month, will have a say in this. Bear in mind even hard coated Lexan will be FAR less scratch resistant than glass, so if you use wipers the screen will have a fairly short life span. I am sure someone determined will just pull a Lexan door window out of the aperture.
Not too much help for you in the UK, but we had Shields Lexan for the R34 here in the US. They had the molds for the R34. Made that pretty easy. They had coated and protected front, rear, and door lexan for a decent price.