Australian-born Greens leader Natalie Bennett has launched a scathing attack on the British electoral system after her party secured just one seat in Westminster despite winning more than one million votes nationally.
Speaking after the general election won by the Conservative Party, Ms Bennett said the UK needed to scrap first past the post voting and introduce a proportional system.
"We have a deeply unfair electoral system (in the UK)," Ms Bennett told the BBC on Friday.
"What we need, and what I suspect we'll see, is a huge public campaign.
"The Green Party, if we did have a proportional system, would have 25 seats."
Ms Bennett, who was born and educated in Sydney, acknowledged it would be tough to convince the major parties to support reform which diminished their own power.
It was, she said, like "getting the turkeys to vote for Christmas".
A referendum on the question of introducing preferential voting was defeated in 2011.
But Ms Bennett said change was needed because first past the post resulted in a third of UK voters not voting in 2015 because they felt they couldn't make a difference.
The Greens won 3.8 per cent of the vote on Thursday compared with one per cent in 2010.
But even with 1.16 million ballots the Greens still only retained former leader Caroline Lucas's seat of Brighton Pavilion.
By contrast the Scottish National Party secured 4.7 per cent of the vote (1.45 million ballots) but because they were concentrated in Scotland won 56 seats in Westminster.
The populist UK Independence Party (Ukip) sits at the opposite end of the political spectrum to the Greens but is also calling for first past the post to be scrapped.
Nigel Farage quit as leader of Ukip - at least temporarily - after failing to win a seat on Thursday, but as he departed he labelled the current system an affront to democracy.
Ukip secured 12.6 per cent of the vote nation-wide (3.88 million ballots) but, like the Greens, has just one seat in the new parliament.
"We gained nearly as many votes as the SNP, the Liberal Democrats and Plaid Cymru added up together," Mr Farage wrote in the Independent newspaper.
"But only one Ukip MP has been returned to the House of Commons - a situation which most reasonable people would realise highlights the flawed nature of Britain's electoral system."
Analysts suggest that under a proportional system Ukip would have won 83 seats in Thursday's poll.
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