The inquiry announced by Theresa May last week into Ronald Waterhouse's original investigation of child abuse in north Wales care homes should be dropped, peers have said.
Ministers announced the probe into whether the Waterhouse inquiry last week, after victim Steve Messham alleged a senor Tory was among the paedophiles involved.
The original inquiry was criticised in some quarters for not looking at allegations of child abuse outside the care homes.
Messham has subsequently apologised for the case of a mistaken identity, triggering the resignation of George Entwistle as BBC director-general.
Now peers are calling for the inquiry into Waterhouse's work to be withdrawn or amended.
Crossbench peer Lord Lloyd of Berwick, a retired judge, suggested that "there is no longer any need for another high court judge to go over the word done by Sir Ronald Waterhouse and that on the contrary we should all be grateful for the impeccable nature of his inquiry and the thoroughness of his report".
Lord Mackay of Clashfern, an advocate and Tory peer, said he viewed Waterhouse as a "very distinguished, conscientious judge" whose work was being unfairly impugned.
"I was in touch with him when he was doing his inquiry and I know the terrific effect it had on him from the harrowing nature of his work," he told the Lords.
"I feel very strongly it is utterly wrong to cast aspersions on his work, unless there is a basis on doing so on which one can rely upon."
Baroness Butler-Sloss, a retired English judge, said the government had "cast aspersions" upon Waterhouse's report by inferring he "didn't do a good enough job".
She suggested that the terms of reference for Mrs Justice Macur's inquiry into Waterhouse's work of the late 1990s be amended.
"If the terms of reference are changed, to say any allegations not made to Sir Ronald Waterhouse should be investigated, I suspect the House would be a great deal happier," she added.
Justice minister Lord McNally said the government would not abandon the Macur inquiry.
"The situation that we faced was not just a single individual coming forward, but a large amount of accusations being bandying around and a great deal of public concern," he told peers.
"I do not think anything the prime minister or the government does calls into question the integrity of the Waterhouse inquiry.
"The review… will look at whether any specific allegations of child abuse were not investigated. The serious allegations that have been made do merit a further thorough investigation."
Labour frontbencher Baroness Smith of Basildon repeated her party's call for an overarching inquiry into allegations of historic child abuse, following claims relating to BBC presenter Jimmy Savile.
Lord McNally said the government was not planning on changing its approach, adding: "I really do not accept that [Mrs Justice Macur's inquiry] impugns either the integrity or the processes of the original report.
"We are indebted to the senior judiciary for so often being willing to take on these very difficult tasks on behalf of society as a whole."
Waterhouse's report, Lost In Care, was published in 2000 after three years of evidence from 259 complainants in Clwyd and Gwynedd.
It identified 28 individuals alleged to have been paedophiles, but did not name any of them.
The report made 72 recommendations, including the establishment of the children's commissioner for Wales, and led to 140 compensation payments to victims.