(1)Every prisoner sentenced by any court to imprisonment …F1 [F2, or ordered to be detained in a young offenders centre] or committed to a prison on remand or pending trial or sentence or otherwise shall be deemed to be in the lawful custody of the governor of the prison in which he is detained.
(2)A prisoner shall be deemed to be in lawful custody while he is confined in, or is being taken to or from, any prison and while he is working, or is for any other reason, outside the prison in the custody or under the control of an officer of the prison or while he is temporarily detained, pending trial or sentence, in any lock-up [F3 and while he is being taken to any place to which he is required or authorised by or under this Act or the Treatment of Offenders Act (Northern Ireland) 1968 [1968 c.29] to be taken, or is kept in custody subject to and in accordance with any such requirement or authorisation].