Inquests that are deemed a risk to national security by the Government would be held in secret in future under proposed powers to come before the House of Lords this autumn.

The provisions, under a clause in the Counter-Terrorism Bill, allow the Home Secretary to stop a jury being summoned, replace the coroner with a government appointee and bar the public from inquests if it is deemed to be in the public interest.

It could be applied to inquests similar to those into the deaths of the weapons inspector David Kelly, “friendly-fire” military casualties or Diana, Princess of Wales, and Dodi Fayed. In future, inquests similar to that into the death of Jean Charles de Menezes, which is due to start next month with 44 police officers giving evidence anonymously, could also be subject to the secrecy clause.

Lawyers, opposition MPs and pressure groups have told The Times that the move represents a fundamental breach of the right to a public inquiry into a death – a centuries-old mainstay of British justice.

They said that a full-scale campaign is being prepared to block the provision, which granted the Home Secretary unprecedented powers to intervene in the workings of the judiciary.

The measure, Section 63 of the Bill, passed through the House of Commons in July without fanfare as debate raged over the headline power for the 42-day detention of terror suspects.

It would enable specially vetted coroners to sit in private without a jury when there is evidence involving national intelligence to be heard, or any matter that the Home Secretary deems not in the public interest.

The family of Azelle Rodney, who was shot seven times by the police in a surveillance operation in April 2005, have been told that their case will be subject to the new measures. The family’s solicitor described the move as a fiasco, bearing no resemblance to a fair system of justice.

The Coroners’ Society condemned the measure as an absolute disgrace, saying that the system could be abused to draw a veil over politically inconvenient cases. The pressure group Inquest added that the proposals would give unprecedented powers to the Secretary of State to intervene in inquests where issues of state intelligence are involved.

John Cooper, a barrister who has acted for families in several inquests, said that there was a great risk that the Home Secretary would accede to holding inquests in private “where matters to be raised are merely embarrassing for the Government”.

He said: “The power could be used to undermine a basic fundamental principle of English law – that of open justice.”

Dominic Grieve, the Shadow Home Secretary, said that the Conservative Party would redouble its efforts to amend the Bill in the Lords. “The Government has so far failed to make the case for handing it the power to appoint the coroner, disband the jury and hold inquests in secret,” he said.

David Howarth, the Liberal Democrat spokesman on home affairs, said: “These proposals are completely wrong. They allow the Secretary of State to remove a case from a jury on the vague ground that it is in the public interest – the whole thing is an appalling violation of the separation of powers.”

A leading Labour MP has also led opposition to the move to scrap the secret inquests measure. Andrew Dismore, the chairman of the Joint Committee on Human Rights, said that the provisions went way beyond mere terrorist cases. He said that they contravened the European Convention on Human Rights.

A spokesman for the Ministry of Justice said the Government recognised that in a “very small number of cases a change to the law may be required to enable inquests to go ahead where highly sensitive material is relevant.

“These proposed changes will ensure inquests are as thorough as possible by ensuring that the coroner can always examine all material central to the inquests even if the material cannot be disclosed publicly. They will ensure families can have absolute confidence in the conclusion the coroner reaches because the coroner will have had access to all the evidence.”

Matters of life and death

— The office of coroner dates from 1194, evolving over eight centuries from medieval tax gatherer to independent judicial officer

— The system was created in its present form in 1887

— There are more than 120 coroners in England and Wales

— They investigate more than 200,000 deaths a year and hold inquests into some 25,000

— They are judicial officers who must have legal or medical qualifications – some have both

— The proportion of all registered deaths reported to coroners was 45.7 per cent in 2006

— In 2006 the most common verdicts returned were deaths by accident or misadventure (34 per cent), natural causes (25 per cent) and suicide (12 per cent)

— In 2006, male deaths accounted for about 68 per cent of verdicts; but included 93 per cent of verdicts of death from industrial disease, 77 per cent of suicide, and 84 per cent of death from dependence on, or non-dependent abuse of, drugs. For females, the most common was death by accident or misadventure (40 per cent of all verdicts for females) and death from natural causes (28 per cent)

— In Scotland the Procurator Fiscal investigates sudden and unexplained deaths

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