Ministers say the measures are needed to prevent intelligence material handed over by friendly governments being disclosed in open court.
On Tuesday, his chief lawyer, Josef Gräsaid-Münscher, said that any material handed over by the Americans would be tainted because it might have been obtained through torture.
Elsewhere, the French finance minister, Michel Sapin, appeared to cast doubt on assertions by the Treasury and HMRC that British prosecutors' hands were tied by limitations placed by France on the use of the material handed over in 2010.
Mr Dunn said the only other material handed over to the US Department of Justice was that of former IRA member Dolours Price, following a court ruling.
The material was handed over on lawyers' advice by News International to the police in mid-June, and shows at least £100,000 mainly in cash was paid to between three and five officers for information.
That material was handed over following court battles on both sides of the Atlantic.
Writer Ed Moloney and republican researcher Anthony McIntyre, who carried out the interviews, are trying to stop the material being handed over to the British authorities.
In November 2012 the material was handed over to Prof Laura Hokkanen, PhD., by a written agreement by Dr. Katarina Michelsson, MD, PhD.
The material would be handed over in electronic format – most probably on CD-Rom discs – and a redacted version may be available later to the complainants.
The Kennedy files were clearly marked among the 1,246 pages of material that police handed over to the CPS between 17 November 2009 and 20 October last year.
