Suspects could be detained in prison without knowing the reasons if the ancient writ of habeas corpus is trumped by government plans for secret courts, according to civil liberties campaigners.
But the Ministry of Justice, which is piloting the controversial justice and security bill through parliament, has dismissed claims by the organisation Reprieve that anybody could be held without being told why they had been arrested.
During a late-night debate in the House of Lords, the Liberal Democrat minister Lord Wallace of Tankerness conceded that closed material procedures (CMPs) might be used in habeas corpus claims, raising the possibility that claimants in secret court hearings might not be allowed to see the evidence against them.
The bill extends into civil courts secret hearings, or CMPs, where a defendant or claimant is not permitted to see all the evidence. Ken Clarke, the justice secretary, has defended the move as a necessary method for allowing intelligence material to be exploited in court cases while preventing general disclosure.
Habeas corpus, first used in 1305 during the reign of Edward I, is a writ celebrated as one of the fundamental safeguards of liberty. It is deployed to demand that a prisoner be released from unlawful detention.
During the Lords debate, another Lib Dem peer, Lord Thomas of Gresford, a former judge, asked: "Are actions against the police for wrongful arrest to be defeated by secret evidence? The government should define much more closely the relevant civil proceedings in which CMPs may be applied for … We have not discussed habeas corpus and matters of that sort. I suggest that they should be specifically excluded."
Lord Wallace, the advocate general for Scotland, said: "Cases about a person's release from detention in the UK will generally be in the context of a criminal cause or matter where CMPs [will] not be available.
"But should this not be the case, it is important that all of the material is before the court, if possible, rather than being excluded."
Clare Algar, the executive director of Reprieve, said: "This is a genuinely chilling development. For centuries, habeas corpus has been the ultimate safeguard against wrongful imprisonment by the state.
"Should these proceedings be pushed into secret courts, the possibility emerges that citizens could be detained without the government having to provide an explanation to them of the reasons for their detention. This removes a key safeguard against a British Guantánamo."
An MoJ spokesperson said: "You can't hold people in detention without informing them why they are there."
CMPs will not be used in criminal proceedings.
