The proposed law is children under 1.35m AND 11 years or younger. People are latching onto the "11 year old" thing and thinking its a draconian law, but its obvious really when you see a child that's too short with the shoulder belt across its neck.
My 6 year old is a bit > 1.35 and doesn't sit on a booster, and the rear seat belts in our car looks just right on him. But my 4 year old daughter is about 1.15 and if she isn't on a booster it looks wrong.
I think the most bizarre thing is that under current laws a 3 year old is permitted to sit in any seat, without any booster!
By the way, we've always used boosters and child seats on leather without a problem - what you need is some of that grey "anti-slip" matting that's sold as a car accessory to stop stuff skidding around in the boot. It works a treat.
Dz