Never realised you were supposed to inform the insurance. My new wheels are running 215/40/18, so I suppose I should give them a ring. I only thought you needed to inform them if you went from steel rims to alloys, or other more serious alterations. Thanks for the heads up.
Have you told them you have changed the size? Its your responsibility to tell them of any changes away from stock. A lot of insurance companies even want factory fitted optional extras declared if you read the small print.
I have declared all my modifications. They didn't care about the size web I told them. Only the value mattered. I have even informed them of the stickers on my car and the fact I will be applying more to go to Le Mans.
If you get a decent insurer with a sensible attitude it's easy to call them and tell them all your modifications. I called recently and told them about my brake upgrade and they said it wouldn't increase my premium at all. They didn't even charge admin fees.
I use Chris Knott.