The Government shall be liable to make good all sums required to discharge any liability which the Administrator-General, if he were a private administrator, would be personally liable to discharge, except when the liability is one to which neither the Administrator-General nor any of his officers has in any way contributed, or which neither he nor any of his officers could, by the exercise of reasonable diligence, have averted, and in either of those cases the Administrator-General shall not, nor shall the Government, be subject to any liability.