Nick Clegg has insisted switching to the alternative vote (AV) would help tackle corruption in politics as he went head-to-head with David Cameron over electoral reform.
The deputy prime minister said under the existing first-past-the-post system MPs in safe seats enjoyed “jobs for life”, meaning they could “ignore” the wishes of large numbers of voters.
“For years now large numbers of people have chosen not to vote because they think it doesn’t matter,” he said during a speech in Leeds. “They think their voice will simply be ignored.”
Mr Clegg admitted it would be “evolutionary rather than revolutionary” if AV was endorsed in the referendum scheduled for 5 May.
But he said it was a “once in a generation opportunity” to bring in change.
“When we have a chance to clean up politics and make our democracy better we should take it,” he said.
The prime minister will spell out his opposition to changing the electoral system later as the leaders make their first major interventions of the campaign.
Mr Cameron is expected to warn that introducing AV would result in more hung parliaments - potentially an awkward argument as both Tory and Liberal Democrat ministers have spent the past nine months extolling the virtues of coalition.
Mr Clegg stressed that the government would hold together regardless of the referendum result.
“It is no secret that the prime minister and I come at this from different directions,” he said. “What we do agree on is that the people know best. We both want as many people as possible to get involved and make their feelings known at the ballot box.
“And what we are clear about is that this referendum is not about the coalition government.
“Whatever the result, we will continue to work together in the national interest.”