"Where (b) an application for the endorsement of the warrant is made to a justice of the peace in the United Kingdom by a constable who produces the warrant and states on oath that he has reason to believe the person named or described therein to be within the area for which the justice acts or on his way to the United Kingdom;
"(1) So soon as is practicable after a person is arrested under a warrant endorsed in accordance with section 1 of this Act, he shall be brought before a magistrates' court and the court shall, subject to the following provisions of this section, order him to be delivered at some convenient point of departure from the United Kingdom into the custody of a member of the police force (Garda Siochána) of the Republic, and remand him until so delivered.