s 12 Rule against double jeopardy
A person’s extradition to a category 1 territory is barred by reason of the rule against double jeopardy if (and only if) it appears that he would be entitled to be discharged under any rule of law relating to previous acquittal or conviction on the assumption— (a) that the conduct constituting the extradition offence constituted an offence in the part of the United Kingdom where the judge exercises jurisdiction; (b) that the person were charged with the extradition offence in that part of the United Kingdom.