Politics
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The party recently stood aside in the Richmond by-election as part of a tactical "progressive alliance" with the Liberal Democrats to prevent a victory for former Conservative MP Zac Goldsmith.
However, they last week decided against doing the same in Copeland because of Labour's decision to field a candidate who was pro-nuclear.
"There was consideration [to stand aside]" Green Party co-leader Caroline Lucas told Business Insider in an interview to be published on Monday.
"But that consideration wouldn't have taken as long as it might have given that the candidate they are going to field is pro-nuclear and that was a big problem.
"The bottom line is that in order to debate progressive alliances you need someone who is pro- electoral reform but I think in addition you need also someone who is passionately pro-nuclear"
Labour leader Jeremy Corbyn has abandoned his life-long opposition to nuclear power since becoming Labour leader. He told a private meeting of his MPs on Monday that he now accepted nuclear power must be "part of the energy mix."
He also signalled that he supported plans to build a new nuclear power station at Moorside in the Copeland constituency.
Lucas, who was once Vice Chair to Jeremy Corbyn as Chair Parliamentary CND, told BI that his subsequent U-turn had been "desperately disappointing".
"Unfortunately the position with Labour right now is we don't know what their position is. Jeremy was pushed really hard on the Marr programme [last week] about Copeland and his position on nuclear. I understand the dilemma that he faces but it is desperately disappointing that you get somebody with those views in a position of influence and he is unable to bring the rest of his party with him."
Our full interview with Caroline Lucas will be published on Monday.