Electoral reform has put a firm divide between the Prime Minister and his Deputy as both traded blows on introducing the alternative vote system (AV).
David Cameron has warned it would be "a massive backward step for accountability and trust in our politics" to bring in the AV system.
But Nick Clegg says it is the only way to tackle corruption at Westminster and prevent millions of voters being "ignored".
Both used speeches on Friday to hammer home their points.
They did agree on one thing. Both men stressed that the result of the ballot on May 5 was not make-or-break for the Government.
Despite senior Tories and Lib Dems extolling the virtues of coalition over the past nine months, the premier also expressed concern that hung parliaments would become "commonplace".
"It won't surprise you to hear me say that this is not necessarily a bad thing and that, as happened last May, it can bring parties together in the national interest," he told an audience in central London. "But let's be clear, when there are more hung parliaments there will be more haggling and horsetrading between politicians - both before and after elections."
Speaking in Leeds earlier, Mr Clegg blamed the existing voting system for encouraging politicians to abuse expenses. "For years, politicians and parties have courted the votes of a few thousand people in marginal seats and ignored the rest," he said.
