Green Party MP Caroline Lucas is to stand for the leadership of her party as part of a job share.
Ms Lucas, who previously led her party between 2008 and 2012, will run for the post jointly with Jonathan Bartley, the party’s welfare spokesperson.
The pair hope to succeed Natalie Bennett, who said she would not be re-standing for leader at the end of her current term this summer.
The MP and her running-mate say they want to build a one-off “progressive alliance” at the next election to defeat the Conservatives.
Such a plan could potentially see the Green Party and Labour standing down in each others’ marginal seats or choosing a unity candidate in order to beat the Conservatives.
A suggested condition of such a pact has been electoral reform and the introduction of proportional representation.
Ms Lucas said job sharing for the role would allow her to focus on her constituents in Brighton while leading the party.
“Jonathan and I are seeking nominations as co-leaders because we believe that by sharing power and working together we'll be more effective than either of us would alone,” she said.
“Over the past 4 years I've become ever more aware that the challenges facing my constituents in Brighton can only be fully addressed by completely changing not just the damaging policies of this Government, but the way we do politics itself. That's why our bid for leadership is centred on going beyond politics as usual.”
Mr Bartley said the Greens could stand down in a “handful” of seats in exchange for political reform but only if local parties agreed the move.
“The one-off 2020 progressive pacts we're talking about must be done on a case by case basis, as agreed by local parties – and will have at its core a commitment to a fair voting system,” he said.
“If it happened it would only be in a handful of seats – but it could make all the difference. Time is up for the two-party system – we want to seize this moment to create a new kind of politics.”
Mr Bartley stood in South London’s Streatham constituency in 2015, gaining around 9 per cent of the vote – up 7.1 per cent.
Ms Lucas is the MP for Brighton Pavilion. She was first elected in 2010 but in 2015 increased her majority to around 8,000 votes.
Green Party leaders are elected on two year terms. The post was created in 2007; before that point the party had two “principal speakers”, one man and one woman.
At the last election the party won 3.8 per cent of the vote and over a million votes. This was up from 265,000 votes and 0.9 per cent in 2010, though the party stood in more seats than it previously had done.
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