Caroline Lucas, Green Party leader and the UK's first Green MP, today issued a firm warning about "the Lib Dems' tendency to backtrack on promises" and called on Nick Clegg to insist on serious electoral reform as a precondition for any coalition deal with David Cameron's Tory party.
Caroline Lucas MP said today: "Nick Clegg has a unique opportunity to make history. Most people in politics are familiar with the Lib Dems' fickleness, but this is the one time when the Lib Dems must hold their nerve.
"Nick Clegg must not wobble. If he fails to insist on genuine electoral reform, he will quite possibly condemn the UK to many more years under an archaic and unfair election system."
During the general election campaign Ms Lucas said the Lib Dems were "not the party of change, but the party of changing its mind."
Green Party role in a hung parliament
The Green Party leader has not yet said what role she may be prepared to play in a progressive coalition should the Conservatives and Lib Dems fail to reach agreement - but it is understood that in any case the new Green MP would want to play a constructive role in fighting for electoral reform.
In a statement issued on Saturday Caroline Lucas laid out her position:
"These are uncharted waters for all politicians. But this only makes it more important that Nick Clegg makes his decisions based on the clear steer given to him by voters.
"In this election, the British people have brought in a House of Commons in which a majority of MPs are from parties which support reform. A clear majority of people in the United Kingdom voted for reform of our political system.
"Therefore, any arrangement between the Liberal Democrats and Conservatives must include genuine and comprehensive reform of the political system.
"A commission, inquiry, or any other delaying tactic will not be acceptable. There should be a referendum before the end of the year which includes options for a genuinely proportional system, not the self-serving system of AV, which is even less proportional. The people should be asked what voting system they would prefer. That is proper democracy.
"The first-past-the-post system has created a situation where people cannot vote positively for the candidate, or party, whose policies they most agree with. Instead, they are forced to vote in fear, working out how to vote to keep out the party furthest away from them in policy and values. This leaves us a grotesque democratic deficit and a poor basis on which to govern.
"The Liberal Democrats must not be seduced by the trappings of power. The people have voted for reform: Nick Clegg must not betray them."