David Cameron's claim he was not aware of serious allegations linking Andy Coulson to a convicted criminal "does not add up", Ed Miliband said today.
The Labour leader said the Prime Minister had "questions to answer" after insisting last week he had not been passed detailed information in the run-up to appointing Mr Coulson as his communications director.
Mr Miliband insisted Mr Cameron has failed to explain away claims the Guardian informed his senior aide, Steve Hilton, that Mr Coulson had rehired Jonathan Rees, a convicted criminal, while he was editor of the News of the World.
He said: "The Prime Minister has a whole series of unanswered questions on this issue.
"The most important of those is this question about specific information that was passed to him by the Guardian newspaper, or passed to his staff.
"We don't yet know from Downing Street that chain of events but we do know there was an admission that Mr Hilton, a senior aide, talked to the Guardian about specific allegations about Jonathan Rees, that he was a convicted criminal, that the Guardian had evidence he was still taking payments on behalf of newspaper organisations and he was also on trial for a further offence.
"As I understand it Mr Hilton passed that to Mr Llewellyn (chief of staff). These were very serious allegations.
"Mr Cameron said in his press conference on Friday 'I had no specific information' but he did have specific information, or at least his team of staff had specific information.
"He needs to now explain. I cannot explain the version of events Mr Cameron has put forward.
"What I'm saying is this account of his does not add up.
"The Prime Minister must explain his position because, frankly, his current explanation does not add up."
Mr Miliband said he was pursuing the "normal course of events to make the Prime Minister come to the House of Commons" to answer questions about the claims.
The Opposition is planning to trigger a Commons vote on Wednesday, calling for a delay in the BSkyB takeover.
But the Labour leader said the decision on whether that was still necessary was changing on an "hour by hour" basis.
"I'll have to get back to you on that one," he said.
"If the Government ends up agreeing with me then the point of tabling trying to force them to take this view becomes less relevant."
Mr Miliband also admitted that former prime minister Gordon Brown "did think about a judge-led inquiry".
"It needs to be further pursued as to why that didn't happen," he added.
Mr Miliband called for the judge-led public inquiry into phone hacking to be set up "immediately" so vital evidence was not destroyed.
He said that formally launching the investigation would trigger legal protections that make it a criminal offence to tamper with documents, including those held in Downing Street and by Conservative party headquarters.
The probe must be set up under the Inquiries Act so it can compel witnesses to attend as well as have a remit to examine "unlawful and unethical" practices in the industry, he urged.
"We need to make sure that it is set up immediately," Mr Miliband said. "Any less means there is a risk that evidence will be destroyed.
"As soon as an inquiry is established, tampering or destruction of any documents becomes a criminal offence.
"And that includes any relevant documents in No10 Downing Street and Conservative HQ."
Shadow culture secretary Ivan Lewis has written to Cabinet Secretary Sir Gus O'Donnell raising questions about the way Mr Coulson's appointment was handled.
He called on the civil service head to reveal whether "the Prime Minister or any of his advisers" had discussed "any warnings they had received about Mr Coulson's prior conduct".
Mr Lewis also urged him to "ensure that all records across government, including emails, that are communications from, to or about Andy Coulson are retained and can be examined by the inquiry".