MPs will decide whether to call Labour deputy leader Tom Watson for a grilling over his pursuit of sex abuse allegations against former Conservative minister Lord Brittan.
A defiant Mr Watson has rebuffed Tory calls to apologise to the widow and family of the peer, who died in January without being told he had been cleared of a rape allegation.
Mr Watson has accepted he should not have repeated the comment of an alleged sex abuse survivor that the peer was "close to evil".
But he insisted he was "right to demand the guidelines were adhered to" and that he was doing his duty by passing on information and pressing for an investigation.
Members of the Commons home affairs committee will discuss whether he should be asked to give evidence before it on the issue - a move backed by David Cameron.
The Crown Prosecution Service (CPS) found in July 2013 that there was not enough evidence for a prosecution, but the decision was never passed on to the peer.
The case was reopened last year after Mr Watson wrote to the Director of Public Prosecutions and police later interviewed Lord Brittan under caution, when he was seriously ill.
The Prime Minister said parliamentary panels were "quite rightly going to ask him some questions" and that the Labour MP should "examine his conscience about whether he's said enough so far".
Demands for an apology - including from the peer's brother - came after a senior Scotland Yard officer wrote to Lord Brittan's widow to apologise for failing to tell the family before the peer's death that he had been cleared of allegations that he raped a 19-year-old woman in 1967.
But Mr Watson told Channel 4 News he believed there was "far more to this case than meets the eye" and it should "be a concern for the Goddard Inquiry" into historic child abuse.
"I need to be honest to myself and to people. I believe that I was helping victims have their voice heard, and I don't want to cause more distress than has already been caused."
Asked whether he would speak to Lord Brittan's family, Mr Watson said: "I'm not entirely certain whether that would be productive."
Pressure on Mr Watson was further increased with the release by the BBC of details of a letter obtained by the Panorama programme which he wrote to the Director of Public Prosecutions, Alison Saunders, complaining at the way Lord Brittan's case was being handled.
"I am driven to the unpalatable conclusion that the identity of the alleged perpetrator, Leon Brittan, may in some way have influenced treatment of the case," he was quoted as writing.
"I hope I am wrong, but in my view the case demands your personal attention."
Mr Watson said he had simply "helped amplify" the voice of the alleged victim who felt they were not being listened to.
"It's not unreasonable for me to demand that the criminal justice system does its job, and I've got some experience of trying to make sure that it does do that."
Tory Sir Nicholas Soames described Mr Watson as "the witch-finder general" and said the debate over historic sex abuse by Westminster figures was "running out of hand".
Lord Brittan's brother Sir Samuel Brittan called on Mr Watson to resign.
"Of course he should apologise for unfounded allegations," he told ITV News.
"But I think he should do more, he should apply for a good job as steward of the Chilterns hundreds. That is an office which was (for) anyone incompatible with being an MP - it's the way many MPs use to resign.
"I don't think he knew anything about my brother. I think he was just looking for scandal because he's not intelligent enough to do his proper job as an Opposition MP."