KEVIN Rudd allegedly described Julia Gillard as a "childless, atheist, ex-communist" at an Adelaide pub as he plotted a political comeback a year ago.

Labor frontbencher Kate Ellis and other witnesses have revealed for the first time the "full story" of Mr Rudd's alleged behaviour at Adelaide's Stag Hotel in February last year.

Ms Ellis, a strong Gillard supporter, claims Mr Rudd addressed his assault on Ms Gillard to guests associated with Senator Don Farrell, a Right-faction powerbroker and one of the "faceless men" who brought down Mr Rudd in June 2010.

"I've been wondering how you reconcile your conservative brand of Catholicism with a childless, atheist, ex-communist as Labor leader," Mr Rudd said, according to several witnesses.

But Mr Rudd's spokesman last night said: "These allegations are lies. Mr Rudd was invited to the function by the then premier (Mike) Rann and his wife. Mr Rudd spent the entire evening out with them."

Former South Australian premier Rann said of the evening: "I did not see or hear any inappropriate behaviour or comments by Mr Rudd. Nor did I hear him attack or criticise the Prime Minister or the government."

But Ms Ellis, who referred obliquely to the incident in media interviews last week, told of her "disgust" at Mr Rudd's disloyalty.

"I know for a fact that he was talking down the Prime Minister," Ms Ellis said.

"Kevin Rudd was there at the Stag. He was telling anyone who would listen that it was his mission - that he was going to get his revenge and come back. He should be honest about what he's been doing. And we shouldn't reward that behaviour."

Ms Ellis said guests at the event had subsequently met to compare notes about what Mr Rudd had said that night.

A lawyer - who was present that night and said he was prepared to sign a statutory declaration over the details of the evening's events - said: "He was just on a rampage . . . I was gob-smacked. It was out of control."

"I came away firmly of the view he was going to tear the whole thing down ... (He was) using foul language."

The Adelaide Fringe Festival party was also attended by former SA Premier Mike Rann, who did not witness the exchange, Finance Minister Penny Wong, and Senator Farrell, who was one of the key figures in Mr Rudd's downfall.

One witness at the pub said: "He said he was going to make a comeback. From that point on, for the whole 12 months, he's been texting journalists in the middle of the night. He was telling anyone who would listen this was Kevin '07 - the comeback year."

Originally published as Revealed: Rudd's pub 'rant' at Gillard