Liberal Democrat Danny Alexander has accused the Conservatives of "pandering" to Ukip and seeking a policy of "austerity for ever", only days after he and UK Chancellor George Osborne delivered the Autumn Statement.
The Chief Secretary to the Treasury is the latest senior Liberal Democrat to blast the party's coalition Government partners ahead of the 2015 General Election next May.
"Who would have thought that of the two parties that formed the Coalition, it would be the Tories who would be blown off course?" Alexander wrote in an article for the Daily Telegraph.
"A mix of unfunded tax promises, harsh spending plans, and pandering to Ukip may be born of pre-election panic, but it is not economically credible."
The Inverness MP also claimed that the Liberal Democrats have helped "save Britain from economic chaos" and warned a future Conservative government would give the UK "austerity for ever".
"British people want neither of these," Alexander argued.
"The only way to avoid economic chaos and keep Britain on the right path is to have Liberal Democrats shaping our economic destiny, as we have over the past four and a half years."
The comments come after the Chancellor George Osborne said the Liberal Democrats would cause "economic chaos" in a future government.
Nick Clegg hit back and accused the Conservatives of "kidding" voters and themselves over the scale of cuts they would impose if they win next May.
"I just think the Conservatives are kidding themselves and seeking to kid British voters if they are claiming that it is possible to balance the books, deliver unfunded tax cuts, shrink the state and support public services in the way that everybody wants. It just doesn't add up," Clegg told BBC 1's Andrew Marr Show.
The Prime Minister David Cameron countered Clegg's comments and claimed the LibDem's are "all over the place".
"The Liberal Democrats are all over the place, unable to decide whether they want to stick to the plan or veer off it. And they – like Ukip – would be prepared to prop up a failing Labour government," the Conservative leader wrote in a letter to his backbenchers.
The exchange comes just days after the 2014 Autumn Statement.
The latest opinion poll from YouGov for The Sun has Labour and the Conservatives neck and neck (32% vs 32%) ahead of the vote next may, with Ukip on 17%, the Greens on 7% and the Liberal Democrats on 6%.