Barristers who represent foreign terrorism suspects held in British prisons without trial have expressed concerns about the legal system.
Campaigners have opposed detentions
The Special Advocates are allowed to see sensitive intelligence material but not share details with their clients.
Ten of the barristers were questioned for a report by the legal reform and human rights organisation, Justice.
The criticisms come as nine Law Lords are to rule this week on whether the detention powers are unlawful.
The Anti-Terrorism, Crime and Security Act 2001 (ATCSA), allows Home Secretary David Blunkett to detain without trial foreign nationals he suspects of terrorism.
Eleven men are currently held under the emergency laws.
Special advocates are security-cleared to examine secret evidence relied on by the government in appeals by foreign nationals detained indefinitely under anti-terrorism powers.
But all of the advocates who took part in the study said it was "profoundly difficult" not being allowed to discuss the evidence with the men they represent.
They were only able to discuss material that was in the public domain, which gave "no clue" as to the nature of the real case against the detainees.
The special advocates said much of the secret evidence was so technical they felt they would benefit from expert advice, preferably from a former member of the intelligence services.