Controversial plans to hold more court hearings in secret are a result of intelligence agencies trying to avoid embarrassment in the future, it has been claimed.
Tory MP David Davis, former director of public prosecutions Lord Ken Macdonald and Mail on Sunday journalist David Rose said claims that the reforms are needed to combat difficulties in intelligence-sharing with the US are not necessarily true.
They were speaking at a meeting on the Justice and Security Green Paper, which would see more civil hearings and inquests involving Britain's security services behind closed doors.
The controversial reforms are said to be aimed at improving the way information from the security services, including MI5 and MI6, is handled while protecting national security.
The plans have been criticised by civil rights campaigners and even deemed unfair by the group of specialist lawyers who would be involved in such cases, the Press Association reported.
The meeting on Monday, organised by INQUEST, JUSTICE, Liberty and Reprieve, heard claims that the Green Paper came in the wake of the case of former Guantanamo Bay detainee Binyam Mohamed.
Last week, justice secretary Kenneth Clarke told the Joint Committee on Human Rights that Mohamed's case risked damaging the UK's intelligence relationship with the US amid claims Britain released US intelligence that was not already in the public domain.
"Since Binyam Mohamed there's real concern about whether we are going to get the full-hearted co-operation with the Americans that we do actually need to provide proper security to our population and to our interests," he said.
But Lord Macdonald said he had many "serious run-ins" with American authorities during his time as DPP, including on where alleged terrorists should be tried if they were accused of crimes in the UK and US.
"We used to come under enormous pressure on this issue," he said.
"We had our fights and we would get up and dust ourselves off and business as usual. These are not one-sided relationships. I think threats of that sort tend to ring a bit hollow as far as I am concerned."
He said the Green Paper was "disproportionate and unacceptable", adding: "This is an audacious attack on our justice system.
"It's quite shocking, I think, to consider that is the response, particularly perhaps of some of the agencies, to Binyam Mohamed."
Davis, a former shadow home secretary, told the meeting he had witnessed a "hard-nosed" relationship with the Americans, but said sharing information was "as much in their interests to keep it going as it is in ours".
"Not only are British agencies embarrassed by criminal action, so are American agencies."
Rose said he was told by a US official that the relationship between the CIA and its British sister agencies had not deteriorated, in contrast to Clarke's claims last week.
Rose said the Green Paper was based on a "misconception" that the relationship had been affected by the Mohamed case and would be affected further if the law was not changed.
He quoted from the paper that there was "already evidence that the flow of sensitive material has been affected".
But he told the meeting he had spoken to someone who could only be quoted as "a US official authorised to speak with the media", and had asked if there had been a deterioration in the relationship as a result of the case.
He was told: "There has been no deterioration in the relationship which remains as strong as ever."
Rose said the argument was not about the sharing of information, but added: "It's that MI5 never wants to go through that (the Mohamed case) again."