Section 21

Any person who, having been sentenced to detention under this Act, is at large may (without prejudice to any other power of arrest) be arrested by any police officer without warrant and taken to any place in which he may be required to be detained in accordance with this Act or any of its regulations.

Where any person sentenced to detention under this Act is at large at any time during the period for which he is liable to be detained in pursuance of the sentence, no account shall be taken, in calculating the period for which he is liable to be so detained, of any time elapsing after he was at large and before he is taken into custody or he is received into a detention barrack.