A Press summary of the decision has been published as well as the court's judgment delivered by Lord Mance.
The Supreme Court noted that Article 38 of the convention enabled the E Ct HR to request the UK government to furnish additional information. Lord Mance said (para 33) - " ... in deciding whether to order that material withheld by governmental authorities from an alleged victim should be disclosed to it, the European Court of Human Rights will consider the independence and thoroughness of the domestic procedure for reviewing the authorities' decision. It will consider in that light whether any and if so what further disclosure should be made. It will by no means necessarily conclude that any further disclosure was required."
Even if refusal to permit disclosure to the ECtHR breached an international obligation, English courts would not be obliged automatically to give effect to such obligation. The UK takes a dualist approach to international law (para 35). The starting point when considering a general discretionary common law power is that domestic and international law considerations are separate. The decision-maker may take international law obligations into account but is not bound to do so.
It remains to be see whether the European Court of Human Rights (E Ct HR) will now be invited to determine whether Article 34 of the convention has been breached.
The Guardian 16th December - Jailed MI6 informant blocked from taking case to court of human rights