Government plans to extend the use of secret hearings in courts are not compatible with the Human Rights Act, the equalities watchdog has said.
Plans to extend the use of secret evidence “are a departure from this country's traditions of open justice and fairness”, the Equality and Human Rights Commission (EHRC) said.
But the Cabinet Office said courts have found “time and again that closed material proceedings can be fair and can bring justice to an area of the law where currently there's none”.
The EHRC's verdict comes after the body examined the widely criticised Justice and Security Bill under its statutory duty to monitor and advise on proposed changes of law to ensure they meet human rights standards.
John Wadham, the watchdog's general counsel, said the process to extend so-called closed material procedures was “incompatible with the Human Rights Act”.
“The Government's proposals to extend the use of secret hearings to civil cases are a departure from this country's traditions of open justice and fairness,” he said.
“The process is incompatible with the Human Rights Act and the principle of a common law right to a fair trial and there is no real evidence to show how the proposals would improve the justice system.”
Under the Bill, judges will be able to listen to more civil cases in secret without claimants being able to hear the evidence against them.
A Cabinet Office spokeswoman said: “Courts have found time and again that closed material proceedings can be fair and can bring justice to an area of the law where currently there's none.
”It means courts will be able to hear cases - and see all of the evidence - regardless of how much information relating to national security is involved.“
There was an explicit statement in the Bill that it must be read in parallel with Article 6 of the European Convention on Human Rights, the Cabinet Office added.
The EHRC's verdict also relies on legal advice which says the most senior judges in the land made a mistake in their most recent judgment on the procedures, it said.
But special advocates, the lawyers who would be involved in the cases covered by the proposals, have said key safeguards were missing and the plans would create a statutory straitjacket for judges.
Human rights group Amnesty also said it showed the Government wanted a ”secret justice system straight from the pages of a Kafka novel“.
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 payout last November after they claimed they were mistreated by US and British security and intelligence officials.