It is for the new press regulator to decide whether a newspaper "sting" operation that forced a minister to resign in a sex scandal was legitimate, David Cameron has said.
Ipso chairman Sir Alan Moses is being questioned at the Conservative Party conference this morning amid Tory anger over the treatment of Brooks Newmark and other MPs.
Civil society minister Newmark, a married father of five, resigned at the weekend after it emerged in the Sunday Mirror that he had sent explicit pictures of himself on Twitter.
The "honey trap" operation involved a fictitious party activist called "Sophie Wittam" who flirted with MPs via social media.
Fellow Conservative MP Mark Pritchard, who was also targeted, has said he is making a complaint to Ipso, and Scotland Yard over alleged entrapment.
Cameron repeatedly declined to offer a view when he was asked for his verdict on BBC Radio 5 Live.
"I am going to plead the fifth on this," he said.
"There is so much criticism that politicians are trying to push the press round and all the rest of it which we are absolutely not.
"We've got this new press regulator; let's let them make a decision.
"Brooks has done the right thing by instantly resigning and trying to rebuild his relationship with this family."
The Prime Minister did note however that there was "quite a debate here amongst the press and politicians about was it right, was it wrong.
"A lot of newspapers, as I understand it, turned down this story because they were worried that it wasn't justifiable but let's let the regulator have a go."
Pritchard questioned why the newspaper had targeted him as a single man.
"Test for Ipso and Met Police. I will write to both today about Sunday Mirror story. Was the criminal law and Ipso Code of Conduct broken?" he wrote on Twitter.
Fellow MP John Whittingdale, who chairs the parliamentary committee which examines press regulation and is a fellow panellist with Sir Alan at the conference fringe event in Birmingham, said the case raised serious questions about whether or not the journalist's method was a legitimate use of subterfuge.
The Sunday Mirror has insisted the story was in the public interest; however, it has apologised to a woman whose picture was used as part of the operation without her knowledge.
Swedish model Malin Sahlen said she was "shocked" that her picture had been used to attract MPs.
Lloyd Embley, editor in chief of the Daily Mirror and Sunday Mirror, said: "The Sunday Mirror stands by its story relating to Brooks Newmark.
"Subterfuge was used in this investigation – and we have been very clear about that from the start.
"We strongly believe there was a clear public interest because of Mr Newmark's roles as Minister for Civil Society and co-founder of Women2Win, an organisation aimed at attracting more Conservative women to Parliament.
"The investigation was carried out before the Sunday Mirror's involvement. We thought that pictures used by the investigation were posed by models but we now know that some real pictures were used.
"At no point has the Sunday Mirror published any of these images but we would like to apologise to the women involved for their use in the investigation.
"We have already spoken to one of them who would like to tell us her side of the story. This will be appearing in this week's Sunday Mirror."
Pritchard told BBC Radio Shropshire: "This is a test for the new standards organisation Ipso to see if it's got teeth and it's prepared to act against its own, because it's still self-regulating.
"I wasn't caught up in anything, but that's not the point.
"What if I'd sent, not an inappropriate text … but said 'hey, let's go out to dinner'? You know, I'm single. So what? What's the news story? It's nobody's business."
"The fact is I wasn't caught up in it, but I have to question some of the techniques used."
He went on: "The old Fleet Street journalism is in the process of cleaning itself up. The majority of journalists I deal with are professional and ethical, and while I agree with a free press, that needs to be balanced, it needs to be accurate and it certainly needs to be lawful.
"Once again, some parts of the British press have got it wrong and got it wrong spectacularly".