Federal Labor MPs have lined up to support Opposition Leader Bill Shorten following claims former party powerbroker Mark Arbib believed he was untrustworthy.

The claim was made by Gerry Kitchener, an adviser to former prime minister Julia Gillard, in the ABC documentary The Killing Season.

Mr Kitchener told the program that during a conversation about Ms Gillard’s ministry, Mr Arbib warned against trusting Mr Shorten.

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“He said that you couldn’t trust Bill Shorten – that he would do Julia in,” Mr Kitchener said.

“[Arbib said] the one thing she couldn’t do was give him industrial relations [portfolio] because he would use it to solidify the union base to knock her off.”

But Labor backbencher Tim Watts has defended his leader.

“I trust Bill Shorten completely,” he said.

“The caucus that I’m a member of is the most united Labor caucus that I can ever remember.”

Prime Minister Tony Abbott makes his point during question time. Photo: AAP

Shadow attorney-general Mark Dreyfus described the program as a “fascinating piece of, I’d say, Australian historical television”.

“That’s what it is, it’s history,” Mr Dreyfus said.

“I know that there are people who will be wanting to make this television program yesterday and perhaps next week’s episode current affairs, but it’s not current affairs, it’s a piece of history.

“Bill Shorten has done an extraordinary job as Opposition Leader to get Labor into and to keep Labor in the competitive position that we have been now in for almost the whole term of the Abbott Government.”

Mr Shorten declined interview for The Killing Season program.

Abbott leaps on ‘untrustworthy’ quote

Mr Shorten started Question Time inquiring about the Government’s deal with the Greens to change pensions, asking: “How can Australians believe a single word this PM says?”

“I am a little surprised that the Leader of the Opposition should choose to start Question Time today talking about trust given what we were told on The Killing Season last night,” Prime Minister Tony Abbott said.

“I want to say publicly thank you to the ABC,” he added as he looked up at the press gallery.

“I don’t normally say thank you to the ABC, but I have to say Australia is indebted to you on this instance.”

Liberal frontbencher Christopher Pyne added: “Rudd and Gillard couldn’t trust you, Arbib didn’t trust you, and he would know because he knocked off three premiers.”

Last night’s episode of The Killing Season suggested Ms Gillard gave tacit approval for other Labor figures to move against Kevin Rudd in 2010.

Interviews with her former staff and various Labor frontbenchers contradicted the picture Ms Gillard has long painted of herself as an unwilling leader, only contemplating change at the last minute when the party’s backroom men said it was her or political death.

But one of Mr Rudd’s allies at the time, Martin Ferguson, said Ms Gillard went as far as discussing opinion polling with him on a flight from Melbourne to Canberra.

Ms Gillard rejected the claim.

ABC