The federal opposition today accused Prime Minister John Howard of trying to gag public servants on the children overboard controversy.

Opposition Leader Simon Crean said the Senate inquiry into the issue must present the facts, but could not be open unless public servants were questioned.

"When questioned (this morning) as to whether he (Mr Howard) would allow all public servants called to appear before the Senate, he wouldn't guarantee that they would be allowed," Mr Crean told reporters.

"Now this is a prime minister that says he wants all facts in the open.

"What he's now trying to do is to gag public servants.

"We've got to get to the bottom of it and it's essential that all public servants called be allowed to attend, speak freely and openly and establish the true state of affairs."

Two reports have shown that within two days of the government claiming asylum seekers had thrown children from a boat into the ocean, official defence sources had confirmed the claims were incorrect.

Mr Crean said there were serious questions at the top of Mr Howard's department.

"I think the question is did (Prime Minister and Cabinet Department secretary) Max Moore-Wilton know of this information? Did the information get to him."

Mr Crean said Mr Howard should resign if it's proven he lied about his knowledge of the claims.

He said if public servants did not inform him the original story had been disproved, then that was a result of a politicisation of the public service.

"If that's the case, then a whole lot of heads have got to roll," Mr Crean said.

He said Labor first became aware claims could be false when reports came from defence in November last year, but Mr Howard assured the public he had checked and confirmed his original view.

Former defence minister Peter Reith today backed up Prime Minister John Howard's account of discussions between the pair on the children overboard controversy.

Mr Reith said today that reports of a conflict between his version of events and Mr Howard's were incorrect.

Mr Howard told parliament yesterday that he had spoken to Mr Reith on October 10 and November 7 about the incident in which asylum seekers had allegedly thrown children into the sea off Christmas Island on October 7.

Mr Howard said he had asked Mr Reith if any further evidence was available on the matter.

But a report in The Australian newspaper today quoted Mr Reith as saying that no such conversation had occurred.

Mr Reith said today the report was "demonstrably untrue".

"I'm not contradicting anything he (the prime minister) said," Mr Reith told radio 3AW.

Mr Reith also said he did not believe he had misled anyone on the matter.

A damning report has found no evidence to suggest asylum seekers threw children into the ocean when their leaking boat was approached by HMAS Adelaide in October last year.

But the government stood by the claims throughout last year's federal election.

Prime Minister John Howard today maintained he spoke to former defence minister Peter Reith about claims boat people had thrown children overboard, despite reports Mr Reith denied any talks.

The Australian newspaper reported today Mr Reith denied he had spoken to Mr Howard at any stage about claims that asylum seekers had thrown their children overboard, which were later proved to be wrong.

Mr Howard told parliament yesterday he had rung Mr Reith on November 7 to check the veracity of the reports during the election campaign.

Today, he said he stuck by his recollection and senior staff could verify the fact.

"My very strong recollection is that on the night Of November 7 ... I did speak to Mr Reith," he told Melbourne radio 3AW.

"My recollection is that in the course of my conversation with Peter I did ask whether he had received any advice contradicting the earlier advice, now that's my recollection and that's the basis of the answer that I gave in the parliament yesterday."

Reports tabled in parliament this week showed Mr Reith, the defence department and the prime minister's department had been told more than a month earlier the claims could be false.

Mr Howard said he had not spoken to Mr Reith in the last few days but he remained one of his closest friends and one of the best ministers he had ever worked with.

He said he had not been dishonest and had nothing to apologise for, either to the Australian people or the boat people involved.

"I owe people an apology if I've done something that's wrong," Mr Howard said.

"I will always apologise for having done something wrong, I will always apologise for having made an error of judgment but I think on this occasion I acted according to advice and I don't believe in those circumstances that it's appropriate to do so."

Mr Howard said he did not think his department had acted dishonestly or incompetently.

But he refused to say whether any action would be taken against other public servants involved in the case, saying he did not want to pre-empt a forthcoming Senate inquiry.

However, Mr Howard said it would be inappropriate for him or his ministers to appear before the inquiry, which he said was politically motivated, and refused to say if he would act on its findings.

Immigration Minister Philip Ruddock today dismissed suggestions he should resign over the controversy.

He told ABC radio: "This happened on the seventh of October. The only other time it arose in the campaign in a very significant way was in the last two days of the campaign."

Mr Ruddock said he could not say why he was not immediately told there was no evidence children were thrown overboard after he made a public statement on the issue.

He said it remained clear that threats to throw children overboard were made.

"It's quite clear that if you read the chronology that has been developed by defence that it was a very difficult situation for the crew...and one in which there is evidence that people threatened to throw their children overboard," he said.

Howard should resign if it's proven he lied about his knowledge of claims asylum seekers threw children into the sea, Labor leader Simon Crean said today.

He told Seven's Sunrise program that the cover-up was uncovering.

"This is John Howard's best and closest mate dumping on him and this is the prime minister's defence yesterday, in tatters," he said. "If it's proven that he lied, he must go."

Mr Crean said he did not believe Mr Howard was not informed that the incident, in which asylum seekers were alleged to have thrown children into the sea on October 7, had not happened.

"Now when the prime minister says he didn't know or wasn't told I quite frankly don't believe him."

He said if it's the case that public servants did not inform him that the original story had been disproved, then that was a result of a politicisation of the public service.

"If that's the case then a whole lot of heads have got to roll," Mr Crean said.