Yep, it can be done in one piece, but only by the best tinting shops. I was talking to the owner of the place who did my tints (Advanced Auto Tinting Centre in Glasgow), and he was saying that although they do it in one piece, everywhere else (including Pentagon) in Glasgow do it in two, or even three, sections, and this can cause problems (peeling away, dust, etc.). Magma seem to be the best place in Edinburgh/the east. Its worth paying a little more if you can find somewhere able to do it in one piece.