Can anyone recommend a mobile window tinting company in berkshire? or someone that covers berkshire?

and does anyone know if I'm allowed to have dark smoke (apparently 40%) on the drivers window, passenger window, and the rear window?

From what i can gather, I'm not allowed to put dark smoke on the front windows, but can I not just tell the plod that they were fitted before January 2004? or will the window tint firm not even do it?

Any advice appreciated