The Prison Act,1894
Section 55. Extramural custody control and employment of prisoners
A prisoner, when being taken to or from any prison in which he may be lawfully confined, or whenever he is working outside of is otherwise beyond the limits of any prison in or under the lawful custody or control of a prison-officer belonging to such prison, shall be deemed to be in prison and shall be subject to all the same incidents as if he were actually in prison.