Section 21.
1The Secretary of State may release on licence a person sentenced to corrective training or preventive detention after he has served such portion of his sentence as may be determined in accordance with rules made under section fifty-three of this Act or at any time.
2A person shall, after his release on licence under paragraph 1 of this Schedule and until the expiration of his sentence, comply with such requirements as may be specified in the licence, including, if the Secretary of State thinks it expedient, a requirement that he shall be under the supervision of such society or person as may be so specified :
Provided that the Secretary of State may at any time modify or cancel any of the said requirements.
3If before the expiration of his sentence the Secretary of State is satisfied that a person released on licence under paragraph 1 of this Schedule has failed to comply with any requirement for the time being specified in the licence, the Secretary of State may by order recall him to a prison; and thereupon he shall be liable to be detained in the prison until the expiration of his sentence, and, if at large, shall be deemed to be unlawfully at large.
4The Secretary of State may release on licence a person detained in a prison under the last foregoing paragraph at any time before the expiration of his sentence; and the foregoing provisions of this Schedule shall apply in the case of a person released under this paragraph as they apply in the case of a person released under paragraph 1 of this Schedule.
5If any person while released on licence, or after he is recalled to a prison, as aforesaid, is sentenced by a court in any part of Great Britain to corrective training or preventive detention, the sentence by virtue of which he is on licence or has been recalled shall cease to have effect; and if any such person is so sentenced to imprisonment or penal servitude, any period for which he is imprisoned under that sentence shall count as part of the period for which he is liable to detention under the original sentence.