The Secretary may from time to time, either generally or particularly, delegate to such officer or officers or employee or employees of the Department as he thinks fit all or any of the powers exercisable by him under this Act, including the power of delegation conferred by this section, but, except as provided in section 44 of this Act, not including any powers delegated to him under any other provision of this Act.

Subject to any general or special directions given or conditions attached by the Secretary, the officer or employee to whom any powers are delegated under this section may exercise those powers in the same manner and with the same effect as if they had been conferred on him directly by this section and not by delegation.

Every person purporting to act pursuant to any delegation under this section shall be presumed to be acting in accordance with the terms of the delegation in absence of proof to the contrary.

Any delegation under this section may be made to a specified officer or employee or to officers or employees of a specified class, or may be made to the holder or holders for the time being of a specified office or class of offices.

Any delegation under this section shall be revocable at will, and no such delegation shall prevent the exercise of any power by the Secretary.

Any such delegation shall, until revoked, continue in force according to its tenor, notwithstanding the fact that the Secretary by whom it was made may have ceased to hold office, and shall continue to have effect as if made by the successor in office of that Secretary.”