One of the UK's most senior judges has slammed a Supreme Court decision to sit in secret for the first time, calling it an "unwelcome departure from the principle of open justice".
Lord Hope, Deputy President of the Supreme Court - the highest court in the UK, said secret justice "at this level" was "really not justice at all".
A panel of nine Supreme Court justices - which included Lord Hope - had concluded in March that a private hearing needed to be held so that material relating to national security could be considered during a case involving an Iranian bank and the Government.
Lord Hope in his office at the Supreme Court in London
And it emerged today, when they delivered a written ruling in the case, that justices had voted to sit in secret by a majority of five to four.
The secret hearing had been staged as Supreme Court justices considered a case in London involving the Treasury and an Iranian bank accused of indirectly helping finance Iran's nuclear weapons programme.
Justices had been told by lawyers representing the Treasury that some material in the case related to national security and could not be safely aired in public.
They spent around 40 minutes behind closed doors - with television cameras switched off.
Journalists, the public, bank officials and lawyers representing the bank were barred.
Two lawyers joined justices at the private hearing. One was a barrister representing the Treasury - the other was a barrister who represented the interests of the bank but was not allowed to reveal what went on to bank bosses.
Lord Hope said he had opposed sitting in secret.
"I was of the opinion ... that it was not open to the Supreme Court to adopt a closed material procedure in this case, as it had not been expressly authorised by Parliament. I remain of that opinion," he said, in the court's written ruling.
"The effect of the decision of the majority, however, is that there is now no way back on this issue. The Rubicon has been crossed."
He added: "The most obnoxious feature of the closed material procedure at the stage of an appeal is the possibility that the appellate court may have to give the whole or part of its reasons for the disposal of the appeal in a judgment to which the State only, and not the other party to the appeal or anyone else, has access."
Lord Hope said secret justice "at this level" was "really not justice at all".
"I very much hope that the Supreme Court will never find itself in a position when it has to resort to the giving of a closed judgment in the disposal of an appeal," he added.
"A stern and steadfast resistance to the use of that procedure would go some way to redressing the unwelcome departure from the principle of open justice that the decision that the Supreme Court may in principle adopt a closed material procedure will inevitably give rise to."
Justices said it "turned out" that there had been "no point" in sitting in secret because there was nothing in the material considered behind-closed-doors that could have affected the court's decision in the case.
Lord Hope said a barrister representing the Treasury had "declined" to give an indication of the "subject matter" of the material relating to national security before justices decided to sit in secret.
He said he suspected that the Treasury "were being over-cautious in their refusal to offer any assistance ".
"The attitude which they have adopted in this appeal was a misuse of the procedure, because they invited the court to look at the closed (material) when there was nothing in it that could not have been gathered equally well from a careful scrutiny of the open (material)," he added.
"This experience should serve as a warning that the State will need to be much more forthcoming if an invitation to this court to look at closed material were to be repeated in the future."
The Iranian bank - Bank Mellat - had appealed to the Supreme Court in an attempt to overturn an order, made by the Treasury under counter-terrorism legislation, which barred it from operating in the UK.
Bank bosses complained that the order was unlawful and unfair - and the Supreme Court today ruled in their favour and allowed the appeal.
Justices concluded that "singling out" Bank Mellat had been "arbitrary and irrational" and "disproportionate".
Bank bosses had earlier failed to persuade the High Court and the Court of Appeal to overturn the order.
When the bank tried to overturn the order in the High Court in 2010, judge Mr Justice Mitting had heard evidence behind closed doors - and delivered a secret judgment based on that evidence.
Neither Bank Mellat, its lawyers, the press nor the public was allowed into the private hearing before Mr Justice Mitting - nor allowed to read his secret judgment.
The Court of Appeal considered that secret judgment before dismissing Bank Mellat's appeal in 2011.
Treasury ministers, who have the power to impose sanctions on anyone involved in nuclear weapons development which poses a ''significant risk'' to the UK, had argued that the Supreme Court could and should consider Mr Justice Mitting's secret judgment before ruling on Bank Mellat's latest appeal.
Bank Mellat had argued that the Supreme Court had no statutory power to consider the secret judgment and did not need to consider the secret judgment when making a decision on whether or not to overturn the Treasury order.
Campaign group Liberty had also argued that the Supreme Court had no statutory power to consider secret material.
Justices had concluded by a 6-3 majority that the Supreme Court had the jurisdiction to consider the Mr Justice Mitting's secret judgment.
They then decided, by a 5-4 majority, that they needed to sit in secret to examine the judgment in order to make a fair decision on Bank Mellat's appeal.
Corinna Ferguson, Legal Officer for Liberty, said tonight: "Proud principles of open justice and the rule of law are the casualties as the secret justice disease infects the highest court in the land.
"Today's chilling judgment brutally exposes the Government's claims and lays bare its willingness to overstate the importance of secrecy to serve its own ends.
"Given recent revelations of spying and snooping it really does seem that it's one rule for the State, another for everyone else - no scrutiny for them; no privacy for us."
Lawyer Sarosh Zaiwalla, a partner at Zaiwalla & Co, which represented Bank Mellat added: "Today's ruling is a victory for the rule of law as much as it is for Bank Mellat. The judgment will put enormous confidence in the independence of the British judiciary and sets the example that even controversial disputes can be resolved by applying the principle of rule of law through the British courts.
"The Supreme Court, after seeing the confidential intelligence evidence produced by the British Government at a secret hearing in court, has found in its judgment that there was nothing in the secret evidence produced to justify an allegation against Bank Mellat and it was not involved in Iran's nuclear proliferation programme.
"This is a finding of fact by the highest court of the United Kingdom and the UK Government, which had originally proposed to the EU Council to list Bank Mellat, will now be compelled to respect this finding of the Supreme Court."
Legal rights charity Reprieve told HuffPost UK they understand that the government intends to attempt to use closed proceedings in the case of Abdul-Hakim Belhaj, an anti-Gaddafi dissident who was kidnapped and ‘rendered’ to Gaddafi’s Libya along with his pregnant wife Fatima Boudchar in 2004 – an operation in which MI6 played a central role.
Belhaj, who is being assisted by Reprieve, has offered to settle his case in return for a token payment of £1 from each of the defendants – the Government, then-Foreign Secretary Jack Straw and former MI6 Director of Counter Terrorism Mark Allen – along with an apology and an admission of what happened.
Commenting, Reprieve’s Strategic Director Cori Crider said: “If the government was prepared to fib about how necessary these secret courts are in a financial case, the risk is tenfold worse when the case involves UK involvement in kidnap and torture.
"We have already seen Government lawyers arguing that they should also be used in the Belhaj case - in short, to cover up the way in which the UK handed Gaddafi his enemies, as part of Tony Blair’s dirty ‘deal in the desert.’ This is a powerful cautionary tale for any court asked to judge torture cases behind closed doors.”