Whenever any portion of the Colony is about to be separated therefrom the Lords Commissioners of Her Majesty's Treasury may if requested by the Governor in Council, on report and accounts furnished by him, declare what portion of the public debt of the Colony has been expended within the territory about to be separated, and the interest and sinking fund, if any, upon the portion of the public debt mentioned in any such declaration shall be a reserved charge payable to the Government of Western Australia by the Government of the separated territory, and due provision for such reserved charge shall be made in any Act regulating the constitution of the separated territory. Provided always, that nothing herein contained, and no declaration or provision as aforesaid, shall in any way prejudice or affect the security of any debentures which may have been issued by the Government of Western Australia before the separation of any such territory.