When news that Mr Melham had quit his post leaked from the Labor Party meeting, one report claimed that he was upset at how Ms Gillard and the executive were treating caucus.

But Mr Melham said his only reflection on Ms Gillard was positive - that he had confidence in leaving his position to someone else (to be chosen at the next caucus meeting) and that the Prime Minister was safe in her job.

He told reporters: ''You have known me long enough in this place. I call a spade a spade, if I had something negative to say, I'd say it to your face.''

Mr Melham has just been re-selected for his Sydney seat of Banks, which is on a margin of less than 3 per cent.

He said the chairmanship involved a lot of work, with ministers continually contacting his office to make sure all legislation was dealt with properly.

Stepping down will allow Mr Melham more freedom to speak out . He has strong views on issues involving human rights and has been pushing for a proper review process for refugees who have adverse security clearances. He said he would take ''a responsible position''. As caucus chairman he had had ''a duty to support the executive''. ''Do I necessarily agree with every single decision caucus has made? Well, I'm from the Left. I'm from the minority grouping.''

Mr Melham voted for Ms Gillard in the February leadership ballot, but would be counted now by Kevin Rudd's camp as in their numbers.

Mr Rudd yesterday said that as PM he had valued Mr Melham's handling of a massive legislative agenda through caucus, including many controversial items. He said he and Mr Melham shared a passion for fair treatment and reconciliation for indigenous Australians, and thanked him for his work in this area.

Ms Gillard, paying her tribute to Mr Melham, said he had expressed ''a completely understandable desire to spend more time in his electorate as we head into an election year''.

In Parliament, Mr Melham was one of the government's speakers opposing the opposition motion for the House of Representatives to dump Peter Slipper as Speaker. Mr Melham, who had nominated Mr Slipper as Speaker on behalf of Labor last year, said he had asked to speak.

He argued that the House should not act in advance of the judgment in the sexual harassment court case now under way against Mr Slipper.

At an impromptu news conference in the parliamentary press gallery corridor, he admitted he occasionally got frustrated at caucus meetings. ''I've got a nickname of 'Grumpy' because I believe in professionalism'' and sometimes Labor Party branch meetings behaved a lot better than caucus.

''Caucus needs to get its act together. We're in government and we need to act like we're in government.''

Mr Melham's successor will be worked out as part of a power-sharing arrangement between Right and Left, with the deputy chairwoman being Yvette D'Ath.

Ms Gillard said she was offended by the Slipper texts ''because I am always offended by sexism''. But a court case was in progress - after that people would have an opportunity to make up their minds with the fullest information available to them.

As she flailed Mr Abbott, Ms Gillard produced a litany of his alleged sexist remarks and actions.