Vote referendum: Clegg dubs AV 'a very British reform'
Changing the electoral system to the Alternative Vote will make MPs work harder and end the scandal of safe seats for life, Nick Clegg has said.
The Lib Dem leader said AV was "a very British reform" and said arguments against it will look "nonsensical" in the future.
But ex-Labour minister Caroline Flint said the current first-past-the-post system had "stood the test of time" and was popular abroad.
The referendum will be held on 5 May.
Voters will be asked whether to retain first-past-the-post or switch to the alternative vote - where voters can rank candidates in order of preference - in the UK-wide poll.
Putting the case for AV in a speech in London, Mr Clegg argued that it was a "very British reform" and represented an "evolution" of the existing system, rather than a "revolution".
Throughout history, voting reform had been opposed by "small-C conservatives", while the No campaign for the referendum is backed by "fascists and extremists" like the British National Party, he said.
Referring to the series of legislative steps which extended the voting franchise in the 19th and early 20th Centuries, the deputy prime minister said a switch to AV would fit into a pattern of constitutional change "by instalments".
In each case, the battle was not between left and right or between particular parties, but between reformers proposing "a reasonable step towards greater representation or fairness" and conservative warnings of "disaster if another step is taken".
"Time and time again, the conservative doomsayers were proved wrong," he said. "The same will be true of AV. The world will not stop turning on its axis when voters write 1, 2, 3 rather than an X on their ballot papers.
"I am certain that in years to come, the arguments being deployed against AV will seem as nonsensical as the ones that were used against allowing women to vote nearly 100 years ago and 18-year-olds the vote 42 years ago.
"It simply brings our system up to date."
But Ms Flint, the shadow local government secretary who is supporting the No campaign, mocked Mr Clegg's "dodgy grasp of history" and his support for AV, which he described as a "miserable little compromise" before entering government.
"The suffragettes fought for One Person, One Vote, not a political stitch-up like AV, which has been rejected by almost every country that has used it," she said.
"One Person, One Vote - the bedrock of our current system - has stood the test of time and remains the only way to ensure elections are fair."
In his speech, Mr Clegg argued that those backing change - who include his party, Labour leader Ed Miliband, the Green Party, UKIP, Plaid Cymru and the SNP - represent a broader cross-section of the population than those supporting the status quo.
And he accused his coalition partners - who support first-past-the-post along with a number of prominent Labour MPs - of double standards, saying the Conservatives use a form of AV in elections for their leadership and to choose certain party candidates.
"It is common knowledge that David Cameron and I disagree about this," he said. "I find it astonishing that the Conservatives say AV is good enough for them but it is not good enough for the rest of the country."