Paddy Ashdown has hit out at the chancellor and his Tory Cabinet colleagues' arguments against the alternative vote, as more evidence of Vince Cable's resistance from within the government emerges.
Former Liberal Democrat leader Lord Ashdown used a comment piece in the Observer to hit out against George Osborne's tactics. He claimed they showed the 'no' campaign was "desperate" as a result.
Meanwhile news emerged that business secretary Mr Cable had encouraged colleges to launch a legal challenge against the government's immigration policy.
"I am very concerned... obstacles are being placed in the way of good business," he told the Sunday Times newspaper.
Lord Ashdown's comments have captured the headlines on Sunday, however, as he attacked the Conservatives for "throwing as much mud as they can to scare people".
He was referring to attacks by Mr Osborne and others against the Electoral Reform Society for funding the 'yes' campaign, while a subsidiary company - Electoral Reform Services - administers the referendum.
Lord Ashdown called the questioning "bizarre". He said Tory chairman Sayeeda Warsi's claim that a 'yes' vote would help the far-right British National party was "as tawdry as it is indefensible".
"The strategy is clear," he wrote.
"Throw as much mud as you can, don't let the issue be discussed openly and frighten the public over the next three weeks into voting to preserve the power the present first-past-the-post system has given you.
"This strategy stinks of the same odour which has surrounded our politics recently."
The 'no' campaign responded by accusing Lord Ashdown of being complicit in a 'cover-up' and reminding him that 'yes' donors expected to profit from AV.
"What is bizarre is that the Liberal Democrats and their 'yes to AV' campaign continue to try and hide what has now been proven as fact: that the largest donors to the Yes campaign also stand to benefit financially from the introduction of AV," Labour No to AV director Joan Ryan said.
"Lord Ashdown is complicit in a cover-up by the Yes campaign at this referendum. He is guilty of the very same thing of which he is accusing the chancellor - namely trying to cover up the truth to preserve (or in this case, advance) his position."
The prominent Lib Dem's attacks come at a time of heightened disharmony between the two coalition parties, as the referendum date approaches.
Mr Cable hit out at prime minister David Cameron's immigration speech on Friday, calling his rhetoric "very unwise" and warning that it risked inflaming extremism.
The parties are working together in government at the same time as they compete in the AV referendum and local elections taking place on the same day.
"In one sense, though, George Osborne makes the case for change for us," Lord Ashdown added.
"He graphically shows why we need to change our politics. Why we need to clean it up. Why the voting public deserve something better."
Frustration in the 'yes' camp in part springs from the closeness of the campaign. A poll by ComRes for the Independent on Sunday newspaper gives the 'no' camp a six-point lead, as the bulk of former 'don't knows' switch to a 'no' vote.