I think I'm happy with the wheel arch extensions I devised (although I'm sure it's been done before). 40mm carbon strip (1.5mm thick). This is bent around into the arch and secured using a number of stainless M4 bolts and nylock nuts. The arch has been shaped to make it flow with the body work, and finished off with some rubber edging. My only concern at the moment is whether the rubber edging is 'round' enough for IVA. As yet I've not studied this part of the manual, but I need to do this....Back up is to use some far thicker edging.
Anyway, end result looks like this:
Also, as you can see the wheels now have a brand new set of R888's on them. I ended up goig to Tiger sports cars for the tyres who got them to me nice and quick, and were very reasonable on cost.