Politics under the first-past-the-post system is "unfair", progressives are arguing before Thursday's referendum on electoral reform.
Labour's John Denham, Liberal Democrat Chris Huhne and Green party leader Caroline Lucas used a comment piece in the Observer newspaper to target the Tory party.
They point out that throughout the 20th century the Conservatives only received the majority of public support twice, but were in government for two-thirds of the period.
"They have divided and ruled," the trio wrote.
"For those who weren't well served by the Tory 20th century, fair votes matter. They matter for the millions of voters who suffered the worst excesses of the Thatcher government, despite more than 54% repeatedly voting against her.
"They matter for the millions of progressive voters, supporters of the Lib Dems, Labour and the Greens among others, who want to be able to express their support for the party of their choice without feeling that they are wasting their vote or letting the Tories in.
"And they matter for the millions who do not bother to vote because safe seats mean they have no chance for a change."
The trio said backing the alternative vote proposed in Thursday's referendum will ensure voters can "back their beliefs", rather than being forced to vote tactically to stop the BNP or Conservatives getting elected.
"It is as simple as 1, 2, 3 but it will be the dawn of an honest age," the article concluded.
"With a system that reflects how Britain actually votes, the progressive majority will be one step closer to reality."
A poll published in the Mail on Sunday newspaper put the 'no' camp 18 points ahead of those supporting 'yes', however, reinforcing former polling impressions that the Yes to Fairer Votes team is struggling to win over the public ahead of this week's vote.
Writing in an article for the Sunday Telegraph newspaper, prime minister David Cameron reiterated his arguments against the alternative vote.
He argued first-past-the-post was worth saving because of its simplicity, effectiveness, efficiency and Britain's history.
"First-past-the-post isn't just one way of counting votes; it is an expression of our fairness as a country," Mr Cameron wrote.
"It is enshrined in our constitution and integral to our history - and AV flies in the face of all that because it destroys one person, one vote."