The full judgment is not yet on the Courts Service website but is available here.
Title: Judge Mahon and Others v Keena and Kennedy,  IEHC 348, High Court, 23 October 2007.
[Update 19 Nov. 2007:
The judgment is now available on the Courts Service website here.]
Cases cited in the judgment include
Oblique Financial Services Limited v. The Promise Production Company 
Kiberd v. Hamilton  2 I.R. 257
Haughey v. Moriarty  3 I.R. 1
O’Callaghan v. Mahon  2 I.R. 32
O’Callaghan v. Mahon (No. 2), Supreme Court, 30th March, 2007
Mahon v. Post Publications Limited, High Court, 4th October, 2005
Mahon v. Post Publications Limited, Supreme Court, 29th March, 2007
Commonwealth of Australia v. Fairfax  147 C.L.R. 39
Sunday Times v. The United Kingdom (1979) 2 EHRR 245
Lingens v. Austria (1986) 87 EHRR 329
Castells v. Spain (1992) 14 EHRR 445
Goodwin v. The United Kingdom (1996) 22 EHRR 123
Dehaes and Gijsels v. Belgium (1997) 25 EHRR 1
Fressoz and Roire v. France (1999) 31 EHRR 28
Tromsov v. Norway (1999) 29 EHRR 12
Radio Twist AS v. Slovakia, European Court of Human Rights, 19th December, 2006
Tonsbergs & Blad A/S v. Norway, European Court of Human Rights, 1st March, 2007
Kwiecien v. Poland, European Court of Human Rights, 9th April, 2007
Ustun v. Turkey, European Court of Human Rights, 10th May, 2007
Ashworth Hospital Authority v. MGN Limited  WLR 2003
Extract from the judgment:
In our view, nothing could be more damaging to the capacity of the Tribunal to carry out its functions than the perception that the Tribunal itself leaked information given to it in confidence. Thus, where a leak occurs as in this case, the Tribunal must inquire to establish the source of that leak as it has sought to do. Establishing that the Tribunal itself was not the source of the leak is in itself a legitimate aim and a pressing social need. At this stage, having regard to the destruction of the documents, the only means remaining to pursue that aim is by way of the proposed questioning of the defendants. If a Tribunal is not enabled to pursue the aim of establishing that it was not the source of the leak, even if it is not able to ultimately identify the source of the leak, the process of public inquiry in private investigative phase will be damaged to such an extent that there would be an inevitable loss of confidence in the integrity of the process and in all probability a significant reductionSample News Story: http://www.rte.ie/news/2007/1023/mahon.html
in the voluntary co-operation of the public in its inquiry.
In the circumstances of this case we conclude that the defendants’ privilege against disclosure of sources, is overwhelmingly outweighed by the pressing social need to preserve public confidence in the Tribunal and as there is no other means, by which this can be done other than the enquiry undertaken by the Tribunal, we are of opinion that the test “necessary in a democratic society” is satisfied.
Accordingly, we will grant the relief sought.
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