Gavin G, you're correct, typo on my part, the tyres are indeed 40's & not 45's.
Chips229, valid point re the camber but I have tested on a very large dead flat expanse if concrete (no drainage channels etc) and the same applies. Don't think the odd tyre wear would support the camber theory either. I think it will have to be the four wheel alignment, anybody know any reasons why I shouldn't take this to my local Lexus garage at Hatfield? I use them for servicing and they're always top notch.