Plans for secret hearings in civil courts are "overkill", a senior Government adviser has warned.
David Anderson, the independent reviewer of anti-terror legislation, said provisions put forward by Justice Secretary Kenneth Clarke remained "disproportionate" to the scale of the problem, and that changes to the Justice and Security Bill had not eased his fears.
Nothing had been done, he told MPs and peers, to address his concerns that ministers, not judges, would decide when to impose secrecy, or to ensure that secrecy would be used only rarely.
He told the Parliamentary Joint Committee on Human Rights in evidence about the Bill: "It addresses what I consider to be a genuine problem, but it does so in a way which is disproportionate.
"I think there is an element of overkill, that I have no doubt will be the subject of debate."
Anderson said he was pleased with some changes made by Clarke following an outcry over the original proposals, such as removing inquests from the scope of the legislation.
But asked if those changes did enough to reassure him that the so-called Closed Material Procedure (CMP) would be used only in cases "of strict necessity", he said: "How to be diplomatic about this? No, no it doesn't."
Anderson said he had been shown details of three cases which had persuaded him there was a problem that would make secret proceedings "tolerable" only in certain circumstances.
But his tolerance was on the condition that CMPs "should be a last resort, to avoid cases that would otherwise be untriable" and that the decision to trigger it "must be for the court and not for the government" – two issues which remained unresolved.
He was also "not aware of any movement at this stage" towards his recommendation that an expert committee should be established to examine the proposals.
CMPs are intended to allow the Government to introduce evidence into court in a secret hearing behind closed doors, in the interests of national security.
The material would be shown to the judge, but would be withheld from the person suing the government, for example, someone claiming they had been tortured overseas by or with the assistance of British agents.
Claimants' interests in such cases would be safeguarded by special advocates – security-cleared and specially trained lawyers who would have access to the material but would be banned from discussing it with the claimant or his or her legal team without permission.
Anderson was particularly scathing of the way the Bill appeared to give judges the final say – as critics had demanded – while in fact leaving them hamstrung and enabling ministers to "continue to pull the strings".
He spoke out after campaigners from human rights group Liberty, dressed as bouncers preventing public access, protested outside the High Court as the House of Lords prepared to debate the legislation.
Anderson told the committee: "I said, and many others said, that the judge should have the last word.
"And in fairness to the Government, under the procedure that's been devised in the Bill, the judge does have the last word.
"The only difficulty is that that word is dictated to the judge by the Secretary of State because the judge can only make a decision at all if the Secretary of State makes an application – he has no other jurisdiction to consider it.
"Secondly, when the judge does come to consider it, it is not for the judge to weigh up the relative merits of PII (Public Interest Immunity) or CMP or to decide what the various ways would be to decide the case.
"The judge's hands are effectively tied: if there is disclosable material that impacts on national security, as I would have thought there pretty obviously will be in any case where an application is made, the judge is required to agree – and the word 'must' features in clause six – the judge 'must' order a closed material procedure.
"So it seems to me they have given formal effect to the requirement that the judge should have the last word, but in substance the Secretary of State continues to pull the strings."
Liberty director Shami Chakrabarti said: "The sight of sinister bouncers barring victims, press and public from a court door may seem unthinkable, indefensible or both.
"But that is exactly what the Justice and Security Bill would achieve – undermining the reputation of Britain's justice system and security establishment in the process.
"The Bill replaces judicial discretion with executive control and destroys the age-old principle that everyone is equal under the law."
A Ministry of Justice spokeswoman said: "We entirely agree with David Anderson that closed proceedings provide a way of scrutinising national security evidence.
"The current rules exclude this material entirely from the courtroom, meaning silence on very serious allegations – no judgment, no questions answered
"The judge will have the final decision that a closed hearing is needed and will then have significant power to ensure that at least the same level of information is available to the claimant as under the current system.
"Nothing heard now in open court could be heard in closed in future under these plans."