The special advocate procedure has received endorsement from the Strasbourg Court: A v United Kingdom  ECHR 301 (19 February 2009).
The special advocate procedure may be resorted to where it is inappropriate to permit a party to the proceedings to know the full extent of the evidence against him. How can the proceedings be made procedurally fair?
Here the issue was whether there were the necessary reasonable grounds to continue the appellants' (referred to as the applicants here) detention under legislation aimed at preventing terrorist activity. The tribunal, the Special Immigration Appeals Commission (SIAC) had full access to the evidence. Some of the evidence was "closed" – not disclosed – and a special advocate was given full access to it in order to make submissions to SIAC on behalf of the applicants to test its reliability. Of course it would be necessary to devise some means of allowing the special advocate to obtain relevant instructions from the applicants. So each case turned on its own facts as far as the issue of procedural fairness was concerned.
The Grand Chamber's remarks on the special advocate procedure are at paras 209-217. The important general principle is in para 218:
"... it was essential that as much information about the allegations and evidence against each applicant was disclosed as was possible without compromising national security or the safety of others. Where full disclosure was not possible, [fairness] required that the difficulties this caused were counterbalanced in such a way that each applicant still had the possibility effectively to challenge the allegations against him."
This does not mean that the party who does not receive full disclosure must be satisfied with a lesser degree of fairness than would otherwise apply.
Here the Grand Chamber found, obviously without going into a lot of detail, that there had been breaches of fairness in respect of some of the applicants. For one group unfairness arose because the link between their financial activities and al'Qaeda was not disclosed so they could not challenge it. For another, the main evidence against them was in closed material and the evidence to which they had access was insubstantial and of no assistance to them in challenging the relevant allegation.
For other references to the special advocate procedure, see the Index to these blogs. An important House of Lords case is R v H  UKHL 3 (pre-dating the start of this site), which I have discussed in "Public interest immunity and fairness to the accused"  NZLJ 301. The special advocate procedure was designed to achieve the absolute standard of fairness to the accused that was required by that case.