The Supreme Court has submitted to what its president Lord Neuberger called the ‘unhappy procedure’ of becoming a secret court to consider some of an Iranian bank’s appeal concerning the validity of a 2009 order made against it by HM Treasury.

The Treasury claimed that privately owned Bank Mellat was involved with Iran’s nuclear weapons development programme and ordered the sanction of forbidding British financial institutions from doing business with it.

The Court of Appeal in 2011 dismissed the bank’s appeal against the order. However, some of the appeal hearing was held in private without the bank or its representatives being present, and a closed judgment was handed down on the grounds of public interest and national security.

The effect was the bank could not know on what evidence its appeal had been dismissed and so was unable to put forward an effective counter-argument. The bank is now again challenging the validity of the sanction order, this time before Britain’s most senior court.

The Treasury lawyers asked the nine judges sitting in the court for this case to look at, and hear brief submissions on, the Court of Appeal’s closed judgment.

In agreeing to the request, Supreme Court president Lord Neuberger said: ‘It must be emphasised that this is a decision which is reached with great reluctance by all members of the court; indeed it is a majority decision.

‘No judge can face with equanimity the prospect of a hearing, or any part of a hearing, which is not only in private, but involves one of the parties not being present or represented at the hearing and not even knowing what is said either at the hearing or in a judgment in so far as it discusses what was said or produced by way of evidence at the closed hearing.

‘Nonetheless, as parliament has decided that, in certain circumstances, such a procedure is necessary and permissible in a trial before a judge, we have concluded that, on an appeal from a decision in a case where a judge has considered closed material and given a closed judgment, it may be necessary for this court to go into closed session in order to dispose of the appeal justly.’

‘No doubt in due course when we have completed the closed hearing and Mr [Michael] Brindle [for Bank Mellat] has made his closing submissions, and we in due course consider the matter and give our judgment, we will have quite a few things to say about this unhappy procedure.’

The case of Mellat Bank v HM Treasury was heard 18-21 March. Judgment will be handed down in around three months.