Chris Huhne, the Liberal Democrat Energy Secretary, has widened an increasingly acrimonious rift in the coalition by threatening legal action over the way the Conservatives have conducted the No to AV campaign.

The No campaign has claimed that the Alternative Vote would cost £250m because it would require electronic counting.

However, the Yes campaign points out that these machines are not used in Australia, which uses AV, and that the Electoral Commission has made no suggestion that the machines would be necessary.

Speaking to the BBC yesterday, Huhne said:

It is frankly worrying if you have colleagues, [whom] you have respected and who you have worked well with, who are making claims which have no foundation in truth whatsoever. If they don't come clean on this I am sure the law courts will.

He added:

That is not good for the coalition. We have a job to do in the coalition government to clean up the mess we have inherited at the time of the last election. It is going to be a lot more difficult if you don't have the same respect for colleagues because, frankly, they have departed so far from the foundations of truth in an election campaign.

The comments follow hot on the heels of Nick Clegg telling the Independent on Sunday that David Cameron was "defending the indefensible" on voting systems, and that the Prime Minister was part of "a right-wing clique who want to keep things the way they are". However, Huhne's comments significantly ramp up the rhetoric on this.

His comments represent the first explicit admission by a cabinet minister that this matter will cause serious problems within the coalition – and that these problems could continue well after the 5 May referendum.

Over at LabourList, Mark Ferguson draws a distinction between the "controlled explosion" of Clegg's comments – clearly co-ordinated to draw a line between the coalition parties – and Huhne's unplanned intervention. This is backed up by a report in today's Times (£), which claims that Clegg is planning to "rewrite the Liberal Democrat role in the coalition" by putting clear distance between the two parties and encouraging his ministers to fight publicly over policy.

However, Ferguson suggests that the Huhne issue is different. He writes:

Huhne wants Clegg's job badly, and he is willing to do whatever it takes to become the darling of his party . . . His renewed fire on the PM is a dramatic escalation of hostilities, and much more important than Clegg's carping at Cameron, because Huhne's anger is real. He doesn't want to be in bed with the Tories. Or if he does, he wants to be in charge.

While it seems unlikely that Huhne will carry through on his threat to resign over the alleged lie about voting machines, he is certainly one to watch over the coming weeks and months. His threat of legal action may remain just that, but the suggestion of concrete action – backed up by Simon Hughes, who suggested that the Yes campaign might refer the matter to the Electoral Commission – implies that the way the referendum is being played will have a great effect on the chemistry of the coalition, regardless of the outcome.

UPDATE 2.20pm: The Electoral Commission has said that it is powerless to challenge the tactics used by the No to AV, as Hughes and Huhne have called for. A commission spokesman said:

As in election campaigns, there is no body with the power to regulate false claims. There is an exception that election candidates are subject to laws barring them from making false claims against rivals. But in a referendum, there are no candidates.