The car is brand new and the calipers are the new spec red ones so I don't really want to be messing them up cos' they look quite good !

i had this problem with my 15s mate. its caused by the shape of the nave(sp) on the wheel. i ground the bits on the caliper that hold the pin back down slightly and that cured it. careful you dont ground too far back though or the spring wont stay on

I don't want to push them further to the arches and risk having to do any arch mods - will wait and try others at Wheelbase - they were very helpful over the phone.

I think if you put spacers on it, it'll make the wheels stick out further, making your offset less but pushing the wheel out so that it wont come into contact with the calipers. The factory 16's which i have on my Sxi now are ET40, so i think in 17's you might be able to go as low as ET42(ish) So 6mm spacers might be ok.

My Kosei 17" Double Racers won't go on my 1.8 SRi. Its not an offset problem, its just that the centre 'hub' of the wheel is bigger than on the factory 16s that are coming off, and they foul the calipers. When they make contact with the calipers, the wheels are still some distance from the hub. The wheels are offset 48 which everyone seems to think would be ok, its just the SRi calipers that are the problem!
Luckily Wheelbase have been very good about it and I'm taking them back next week to get something that does go straight on.