The Extradition (Drug Trafficking) Order 1991

9.  Without prejudice to the exercise of any criminal jurisdiction established in accordance with its domestic law, a Party in whose territory an alleged offender is found shall:

(a) If it does not extradite him in respect of an offence established in accordance with article 3, paragraph 1, on the grounds set forth in article 4, paragraph 2, subparagraph (a), submit the case to its competent authorities for the purpose of prosecution, unless otherwise agreed with the requesting Party;

(b) If it does not extradite him in respect of such an offence and has established its jurisdiction in relation to that offence in accordance with article 4, paragraph 2, subparagraph (b), submit the case to its competent authorities for the purpose of prosecution, unless otherwise requested by the requesting Party for the purposes of preserving its legitimate jurisdiction.