"Without prejudice to any jurisdiction of the High Court apart from this section, the court shall order the applicant's discharge if it appears to the court in relation to the offence, or each of the offences, in respect of which the applicant's return is sought, that - ... (b) by reason of the passage of time since he is alleged to have committed it... It would, having regard to all the circumstances, be unjust or oppressive to return him."