Doesn't your car have a trunk or at least a covered storage area in the back? Pop the wheels off and my bike (60 cm) fits in the trunk of my old Toyota Corolla (i.e. pretty small) so it's completely out of sight.
And if the B&B is designating their utility room as "secure storage" that would seem to put the risk on them if something happens. So any theft should be reimbursed by their insurance.
My experience has been more with hotels/motels where I've generally had no problem just wheeling the bike inside after a ride. The one exception has been hotels in Las Vegas which are deliberately arranged so you can't reach the rooms without first wandering through the crowded slot-machine areas. But they've always offered secure storage where it's retrieved by the valet service upon request.