I thought it sounded odd! I'll have to check out a few other places when they open up on Monday.
Cheers.
Printable View
So I've since been to another dealer and they were nice enough to fit a 17 inch steel rim to my car right there and then.
Turns out it fit with plenty of room over the brake calipers and plenty of space between the steering rods and the rim.
I guess the first place I went too were just trying to sell me some expensive alloys or something....