Prime Minister leads calls for No vote

"I don't think John would mind if I say we don't agree on much but we do absolutely agree on this - AV would be wrong for Britain," the PM explained.

"It is obscure, it's unfair, it's expensive, it could mean that people who come third in elections will end up winning.

The Prime Minister said electoral reform was about "how you feel in your gut, the values you hold dear and the beliefs you instinctively have", admitting "I feel in my gut that AV is wrong."

He warned that power should lie with the people and AV would "take some of that away".

He added: "I believe in the principle of one person, one vote, and AV would mean that votes of some people get counted more than others."

He said AV was "not as decisive" as the first-past-the-post system and if the last General Election had been held under AV, there was a chance that Gordon Brown would still be prime minister.

"I know the last election was not decisive in terms of who won but I think it was decisive in terms of who lost," he said.

"And I think a system that keeps dead governments living on life support is a backward step for democracy."

Mr Cameron said coalition governments could be a good thing in the "right circumstances" but warned that frequent coalitions could be "damaging".

He acknowledged that many voters had so far shown little interest in the debate about voting reform, concluding: "The biggest danger right now is that Britain sleepwalks into this second rate system, waking up on May 6 with a voting system that damages our democracy.

"We must not let that happen so we've got to get out there and fight and we've got to get out there and win." ITN