Image caption Lord Neuberger said the decision was made with "great reluctance"

The UK's Supreme Court has held a hearing in secret for the first time since it was founded in 2009.

The nine justices sitting at the court concluded they had no choice but to hear in private a government case relating to Iran's nuclear programme.

The justices were told that material in the case related to national security and could not be publically aired.

Supreme Court president, Lord Neuberger, said a secret hearing in this case was "absolutely necessary".

The justices spent approximately 45 minutes in a locked session with two security-vetted lawyers. The hearing was so sensitive that the justices had to leave one courtroom and set up in another which had greater soundproofing. A security guard stood outside to prevent anyone trying to enter.

The Supreme Court had decided earlier this week that it had the power to close its doors and consider a secret judgement from the lower courts - but the justices had said they did not want to do so because they did not think it was necessary.

'International concern'

The justices are being asked to overturn a Treasury ban on an Iranian bank operating in the UK.

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 Lord Neuberger

Ministers have barred Bank Mellat from the British financial markets. The government has alleged that the private bank had been indirectly involved in financing companies involved in Iran's nuclear programme.

Mellat appealed to the Supreme Court after failing to persuade the High Court and the Court of Appeal to overturn the order. It says it has been denied a fair hearing.

When the bank originally challenged the government's decision in 2010, the High Court heard some of the evidence behind closed doors because it included material that could not be disclosed on grounds of national security.

As is standard in such cases, the court then delivered two judgements - one of them secret and only available to the government.

During the final appeal to the Supreme Court, government lawyers insisted that the justices must assess the secret judgement if they were considering ruling in the bank's favour.

Bank Mellat's lawyers argued that a closed hearing would damage their ability to put their case fairly, as their legal team would be absent.

Initially, the justices refused to do so until the government provided a public summary of the secret judgement, known as a gist.

Lord Hope said the government's reasons for refusing to put more basic information before the court was "cloak and dagger stuff" that was "difficult to swallow".

But after a majority vote among the nine justices, the judges said they would look in private at the government's case.

'Great reluctance'

Image caption Supreme Court: Final court of appeal in the UK

Lord Neuberger, who two weeks ago told the BBC of his concerns about secret courts, said he and the eight other justices "were dubious indeed" whether the closed judgement would help their decision.

"However... unless and until an appellate court sees the judgment, it often cannot be sure its contents will be irrelevant or that its contents have been fully gisted [summarised in open court].

"We have reluctantly decided that we cannot consider the closed judgment without having a closed hearing.

"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.

"Nonetheless, as Parliament has decided that, in certain circumstances, such a procedure is necessary and permissible."

The decision means the UK's highest court may now produce two judgements in a case - a public ruling and another that will remain secret.

If the court does produce a secret closed judgement, it would only be open to a small number of ministers, their lawyers and security and intelligence officials.

In a statement, Bank Mallet's lawyer Sarosh Zaiwalla said: "Britain is internationally recognised as a beacon of open justice and parties from all over the world come to the UK because of this.

"It is therefore of international concern that the UK Parliament has given the right to the court to use this closed evidence procedure."

He added the bank had "nothing to fear" from the ruling.

MPs have recently separately passed the Justice and Security Bill to expand the use of secrecy in a range of court cases , including damages claims against MI5 and MI6.

That legislation came after Lord Neuberger, in his previous Court of Appeal role, had refused to allow more secret hearings without the approval of Parliament.