Injustice and oppression as grounds for resisting extradition were considered in Gomes v Trinidad and Tobago  UKHL 21 (29 April 2009).
The precedent is Lord Diplock's statement in Kakis v Cyprus  1 WLR 779 (HL):
"'Unjust' I regard as directed primarily to the risk of prejudice to the accused in the conduct of the trial itself, 'oppressive' as directed to hardship to the accused resulting from change in his circumstances that have occurred during the period to be taken into consideration; but there is room for overlapping, and between them they would cover all cases where to return him would not be fair."
How much risk of unfairness is sufficient to create injustice sufficient to resist an order for extradition? The focus is on the proposed trial in the requesting state. The court must decide whether that trial carries an unacceptable risk of unfairness.
Does the court in the requested state have to decide what the court in the requesting state would decide about fairness?
Or, should the court of the requested state make its own assessment of the fairness of the proposed trial in the requesting state?
And, either way, what is the relevance of unfairness of the accused's own making? Is a trial unfair regardless of who caused the unfairness, or is a trial "fair" even if some unfairness to the accused was brought about by his conduct?
Is the "justice" of extradition the same sort of concept as the "fairness" of the proposed trial?
Without looking at the answers, one might think that the court in the requested country should make its own assessment of the risk of what it understands to be an unfair trial, and that for extradition to be refused this risk should be at least the same as that which would be sufficient to stay the proceedings in the requested country. And, unfairness is unfairness, no matter who caused it.
Logical as those suggestions might be, policy requires a different approach.
In Gomes the Report of the Appellate Committee, written by Lord Brown, holds that Lord Diplock had correctly stated the law when he said, following the passage quoted above,
"Delay in the commencement or conduct of extradition proceedings which is brought about by the accused himself by fleeing the country, concealing his whereabouts or evading arrest cannot, in my view, be relied upon as a ground for holding it to be either unjust or oppressive to return him. Any difficulties that he may encounter in the conduct of his defence in consequence of the delay due to such causes are of his own choice and making. Save in the most exceptional circumstances it would be neither unjust nor oppressive that he should be required to accept them."
Additional delay due to the dilatoriness in the requesting state will only be relevant in borderline cases where the accused is not responsible for any delay (27). The blameworthiness of the requesting state is not a matter that will normally be considered, because the accused gets the benefit of any delay that is not his fault (28).
The test for oppression will not easily be satisfied (31), and injustice has to be established in the way held in Woodcock v New Zealand  1 WLR 1979, as approved by Lord Bingham for the Board in Knowles v US  1 WLR 47 (PC):
"First, the question is not whether it would be unjust or oppressive to try the accused but whether . . . it would be unjust or oppressive to extradite him (para 20). Secondly, if the court of the requesting state is bound to conclude that a fair trial is impossible, it would be unjust or oppressive for the requested state to return him (para 21). But, thirdly, the court of the requested state must have regard to the safeguards which exist under the domestic law of the requesting state to protect the defendant against a trial rendered unjust or oppressive by the passage of time (paras 21-22). Fourthly, no rule of thumb can be applied to determine whether the passage of time has rendered a fair trial no longer possible: much will turn on the particular case (paras 14-16, 23-25). Fifthly, 'there can be no cut-off point beyond which extradition must inevitably be regarded as unjust or oppressive' (para 29)."
The first point separates the question of fairness of the proposed trial from the justice of extradition. The second makes relevant the likely view of the court in the requesting state of the fairness of the proposed trial, so that extradition is barred if that court would be bound to conclude the trial would be unfair. Third, the law of the requesting state as to whether the trial would be unjust or oppressive, must be considered.
Gomes holds that the essential question is whether a fair trial would be impossible (33) [Compare USA v Barnette noted here 27 August 2004: a flagrant or gross risk of unfairness will be sufficient to prevent extradition.] Does that mean that a high likelihood of trial unfairness would be insufficient to prevent extradition? Of course the court in the requesting state would stay the proceedings if the risk of unfairness was unacceptably high according to the standards applicable in the law of that state. That is where the third point quoted above comes into play. It may be that the standards applicable in the requesting state would be unacceptable in the law of the requested state. If they were, extradition would be refused.
Does Gomes mean that in UK law, if an accused is responsible for delay which prejudices his ability to present a defence, the trial must proceed even though it would be unfair? Can the right to a fair trial be waived? Perhaps it can, but to the contrary, see R v Coutts  UKHL 39, noted here 21 July 2006. In Coutts, fairness required an alternative verdict be left to the jury, and the accused could not decide that that should not be done. This was not discussed in Gomes.