Such insurances as are necessary to cover the liability of the Contractor, or as the case may be, of such sub- contractor in respect of any injury or damage whatsoever to any property real or personal in so far such injury or damage arises out of or in the course of or by reason of the carrying out of the Works, and provided always that the same is due to any negligence, omission, or default of the Contractor, his servants or agents or of any sub-contractor, his servants or agents