Hi there, and welcome to the forum from one of the other few Brits on here
As a winter project (now stalled due to "New Kitchen Installation" duties
) I have some MGF 15" wheels with 195 & 205 tyres which I test fitted earlier the year. I was expecting some problems at the front as another UK owner with an S2 had mentioned some slight scuffing on full lock, but nope, there was plenty of room in the front wheel arches. I thought the S2 & TC body moldings would be the same in the wheel arches, but clearly not.
Anyway, I'd expect a 185 to be ok, the handbook warning is probably more about the possibility of someone swopping front & rear wheels around and messing up the handling ? Of course the easiest way to be sure is just jack up one side and try it.
Brian (Lincolnshire and freezing cold !)