As both figures fired intense personal attacks, Mr Rudd directly blamed Ms Gillard's policy stumbles for the government's poor ratings, as he officially fired up his campaign to take back the leadership.

''Rightly or wrongly Julia has lost the trust of the Australian people,'' he said yesterday.

''I want to finish the job the Australian people elected me to do when I was elected by them to become prime minister,'' he said.

In her most vicious assault on Mr Rudd to date, Ms Gillard mocked his words on trust and suggested he had folded when the going got tough.

''This is not an episode of Celebrity Big Brother, this is about who should be prime minister,'' she said, referring to his pitch for ''people power'' to influence caucus members.

The Prime Minister said Mr Rudd had ''dragged her down every step of the way'' but was now denying his role in destabilising her government.

''He won't reveal to the Australian people the conversations that he has had undermining the government,'' she said.

Ms Gillard's pitch to caucus is that she has the courage and determination to tackle hard tasks, and had delivered major reforms that had ''languished'' under Mr Rudd.

''I'm someone who gets up every day and does it all again, no matter how hard the going is,'' she said.

''Kevin Rudd, when the going got tough, couldn't get carbon pricing done. In the toughest of all political circumstances I got it done.''

Sharpening the fight for her political life, Ms Gillard said Mr Rudd had a poor record when it came to ''trust''.

''Kevin Rudd spoke about trust today but did not deny when challenged that he has spent time whilst I have been Prime Minister and he has been foreign minister behind closed doors, in secret conversations with people, undermining this government,'' she said.

''There's questions of trust there.''

After formally declaring he would stand against the Prime Minister in Monday's caucus ballot, Mr Rudd accused Ms Gillard of taking a ''walk on the policy wild side'' on asylum seeker policy.

He blamed Ms Gillard and Treasurer Wayne Swan for convincing him to ditch his emissions trading scheme but said he took responsibility for the decision.

Despite his withering assessment of the Prime Minister's performance, Mr Rudd said he would not mount a second challenge if, as expected, he loses the ballot.

''I would go to the backbench and I will not challenge Julia a second time,''' he said.

Mr Rudd appears to have around 30 votes in the 103-member caucus but some of his key backers in cabinet had not openly declared their support by last night.

The ACT's three Labor MPs, Kate Lundy, Gai Brodtmann and Andrew Leigh are backing Ms Gillard.

Parliamentary secretary Mike Kelly, who represents Eden-Monaro based in Queanbeyan, is believed to favour Mr Rudd but will not confirm or deny this.

Despite the bitter divisions being expressed openly, Minister Chris Evans said the party would unite after the ''messy'' leadership ballot.

However, as Ms Gillard referred to the need for the leader to have strength and character, two ministers said they would refuse to work in a Rudd-led cabinet.

Attorney-General Nicola Roxon said Mr Rudd as prime minister had proposed running a referendum on health at the 2010 election while knowing it was likely to fail.

Mr Rudd said he was not to blame for Labor's poor support in the polls and he was not involved with making or breaking the promise on the carbon tax.

''I'm a bit tired and fed up … that ipso facto the problem is me,'' he said.

''The government's problems are not the fault of K-Rudd.''

Mr Rudd said he was not prepared to ''stand idly by'' as Australia elected a Tony Abbott-led government.

''We'll all end up on the backbench, not just one, and the Opposition backbench at that,'' he said.

''That's the cold, hard stark reality that we face.''

Mr Rudd said he had always believed that Ms Gillard's ill-fated East Timor solution, which she announced shortly after she won the prime ministership, would not work.

''Those sorts of things need to be looked through very carefully before you simply take a walk on the policy wild side and find that other governments may not necessarily concur,'' he said.

Mr Rudd said it was ''explicitly agreed'' with Ms Gillard on the night of their leadership discussion that he be given more time to work through the problems the government was facing.

But Ms Gillard had come back 10 minutes later to say she was challenging for the leadership, he said. Mr Rudd said his discussions with journalists would remain confidential but said he had supported the Prime Minister.

Ms Gillard repeatedly said she should remain Prime Minister because of her determination and strength.

''Getting things done is harder [than talk], I am the person who gets things done,'' she said.

She said Mr Rudd had made some ''amazing contradictions'' when he spoke in Brisbane yesterday.

''He had asked people to consider questions of trust, when he wouldn't reveal to the Australian people the conversations that he'd had undermining the government,'' she said.

''What shouldn't happen in politics is you shouldn't be dragged down by someone who is on your own side, who today is unable to deny they have been in conversations behind locked, behind closed doors, talking to people and undermining the government.''

Ms Gillard launched a stinging attack on Mr Rudd's time in the nation's top job. ''What Kevin obviously struggled to do when times were a little bit politically tough, particularly in 2010, was run a government with any sort of method, or purpose, or discipline,'' she said.