The Channel Tunnel (Miscellaneous Provisions) Order 1994

Article 14

(1) In the event that a person is found committing, attempting to commit or just having committed on board a train in the territory of a State one of the following offences: homicide, rape, arson, armed robbery, kidnapping and hostage taking, or use of explosives, the train must be stopped in order to enable the competent authorities of that State to take any measures relevant to their investigations and, where appropriate, detain the person suspected of having committed the offence.

(2) If the train cannot be stopped because it is within the Fixed Link or because it is about to leave the territory of the State in which one of the offences referred to in the preceding paragraph has been committed, authorised officers who are present must take all appropriate interim measures to ensure that, when the train arrives, the officers of the State which has jurisdiction under Article 11 are able to interview witnesses, take evidence or receive information relevant to their investigations and, where appropriate, take charge of the person suspected of having committed the offence.