AV referendum: Huhne 'confronts Cameron at cabinet'
Chris Huhne is said to have confronted the prime minister at a cabinet meeting over the No campaign's claims in the alternative vote referendum.
Sources described a "bit of a bust-up" as the energy secretary "went for" David Cameron and George Osborne.
But both the Yes and No campaigns have criticised Mr Huhne for diverting attention from the main issues.
Voters will be asked on Thursday whether they want to change the voting system for UK-wide elections.
A source from the Yes campaign told the BBC: "Nothing Chris Huhne has done in the last few weeks was authorised by us or useful to us.
"The difficulty from day one was that we didn't want the referendum to be seen through the prism of the coalition."
And a spokesman for the No campaign accused Mr Huhne of using "increasingly offensive and hysterical invective to obscure the issue of AV".
The issue of whether to change the way MPs are elected divides the coalition - the Conservatives want to keep first-past-the-post while the Liberal Democrats are supporting the Yes campaign for the alternative vote.
The confrontation between Mr Huhne and Mr Cameron happened at a cabinet meeting on Tuesday morning.
The energy secretary is understood to have put two leaflets issued by the No campaign - which Lib Dem activists regarded as a personal attack on party leader and Deputy Prime Minister Nick Clegg - on the table.
He then challenged the prime minister and the chancellor to defend them and sack any Conservative activist involved in them.
One source said: "There was a bit of a bust-up. Chris Huhne went for the PM and the chancellor over AV."
The BBC's deputy political editor James Landale said that the chancellor had intervened, telling Mr Huhne: "This is the cabinet, not some kind of sub-Jeremy Paxman interview".
Other sources, James Landale added, suggested Mr Huhne's actions felt like a "deliberate stunt by the Yes campaign" and that he had not been supported by anyone else in the cabinet.
A No 10 spokeswoman confirmed AV "was raised in the context of parliamentary business" at the start of the meeting.
Asked about the confrontation, Deputy PM Nick Clegg said he would not give "a running commentary of what was said in one cabinet meeting" but told the BBC it was no secret "that I feel and other people from the Liberal Democrats" felt the No campaign had been "quite misleading".
It follows an interview with the Guardian on Monday in which Lib Dem minister Mr Huhne accused the Conservatives of "trashing" his party and Mr Cameron of doing nothing to stop personal attacks on Mr Clegg by the No campaign.
Mr Huhne, a former Lib Dem leadership contender, has been one of the most vocal Lib Dem critics of the No campaign's tactics - threatening legal action and comparing claims made by cabinet colleague Baroness Warsi to Nazi propaganda.
But a spokesman for the energy secretary accused Conservatives of "furiously" briefing about the meeting despite a convention that the proceedings remained private.
Ex-Labour minister Lord Boateng decided against criticising Mr Huhne by name in his speech to a No to AV rally, after a pre-released extracts suggested he would, as the No campaign seeks to move the debate away from a row between politicians.
Earlier Mr Cameron distanced himself from the official No to AV campaign's controversial posters which used images of a sick baby and suggested the cost of introducing an AV system could be up to £250m - something the Yes camp disputes.
He told BBC Radio 4's Today's programme he was "directly responsible" only for the official Conservative Party no campaign but he stood by the No campaign's claims AV would "very likely" mean electronic counting machines would have to be bought.
Amid opinion polls suggestions that the Yes campaign is heading for defeat, Labour leader Ed Miliband said he did not accept that the AV result was a "foregone conclusion" - adding: "Let's see what happens on Thursday."
He also defended his decision to refuse to share a Yes campaign platform with Nick Clegg due to his perceived unpopularity with voters: "There's a reason the No campaign want to make Nick Clegg the poster child for their campaign."
The Yes campaign is trailing in the opinion polls, with a survey by The Sunday Times/YouGov putting them 10 points behind - a narrowing of the poll before that, which put them 18 points behind.
But campaigners for changing the electoral system insist it is still all to play for, with turnout in different parts of the country likely to prove crucial.
The No campaign also believes turnout will be all-important. A spokesman said: "At this stage no one can be certain what the turnout is going to be like and it is about getting out your vote."