The Government wants a "secret justice system straight from the pages of a Kafka novel", a leading human rights group has said.
Proposals to extend the use of secret evidence will enable the Government to "simply play the 'national security' card whenever it wants to keep things secret", Amnesty International said.
Its critical 50-page report comes before the Justice and Security Bill, which contains the measures for more "closed material procedures", is debated in the House of Lords over the next few weeks.
Under the widely criticised Bill, judges will be able to listen to more civil cases in secret without claimants being able to hear the evidence against them.
It poses "a real threat to the principles of fairness and open justice in the UK", Amnesty's Alice Wyss said.
"It's already bad enough that secret procedures have been allowed to creep into the justice system but the Government is now trying to extend secret justice to an unprecedented degree. It wants a system where it can simply play the 'national security' card whenever it wants to keep things secret. Evidence that is kept secret, lawyers that can't talk to you: it's a secret justice system straight from the pages of a Kafka novel. The Justice and Security Bill will enable the Government to throw a cloak of secrecy over wrongdoing."
Special advocates, the lawyers who would be involved in the cases covered by the controversial proposals, said key safeguards are missing and that the plans would create a statutory straitjacket for judges. But the Bill's proponents claim it is needed so the Government can contest civil claims in the courts.
The Government has said it is wasting millions of pounds of taxpayers' money on settling claims, some of which may have no merit, because it is unable to contest them as the evidence it would wish to produce is so secret that it cannot be revealed in an open court.
It comes after 16 terrorism suspects, including former Guantanamo Bay detainee Binyam Mohamed, received a multimillion-pound pay-out last November after they claimed they were mistreated by US and British security and intelligence officials.
A Cabinet Office spokesman said: "The point Amnesty have missed is that currently no one, not the claimant, not their lawyers, nor the judge, can take into account or rely on national security-sensitive evidence. The result is that cases collapse and we never get to the bottom of serious allegations made against the state. The Justice and Security Bill will fix this problem by allowing the national security evidence which is excluded under current rules to be heard in a closed procedure. Closed justice is never ideal but it is better when the alternative is silence."