Jo Swinson used her appearance on a follow-up programme to the ITV debate between Boris Johnson and Jeremy Corbyn to argue that the pair’s encounter only went to make the case for the Liberal Democrats.

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In a decision that prompted a failed legal action from her party, Swinson was excluded from the debate at 8pm and shunted to a programme featuring one-on-one interviews with the leaders of the smaller parties, along with Nicola Sturgeon, Nigel Farage and Siân Berry, which aired at 10pm.

Berry, the Green party’s co-leader, also took the opportunity to castigate the Johnson-Corbyn debate, saying it was “outrageous” that the Tory and Labour leaders barely discussed the climate emergency.

Swinson, whose party’s legal challenge was rejected on Monday, told ITV’s interviewer Nina Hossain that the main debate only highlighted the absurdity of her being sidelined. “Watching that debate, people at home can be forgiven for just saying, look, surely we can do better than this, than what was on offer from those two tired old parties,” she said. “We need something fresh, something different and a better choice.”

Asked about her avowal that Lib Dem MPs holding the balance of power would not back a Johnson or Corbyn government, she said: “Liberal Democrat votes are not going to put either Boris Johnson or Jeremy Corbyn into power, because I believe our country deserves better than either of them. And I think anyone watching that debate tonight will surely agree with that.”

Play Video 3:10 Boris Johnson and Jeremy Corbyn clash in ITV election debate – video highlights

Swinson said the notion of the Lib Dems backing one of the main parties if the leader changed was “a hypothetical situation” and argued that the Conservatives and Labour had both long since left the mainstream.

She said: “The Conservative party is so far off to the right, the Brexit party is standing down in half the seats and Tommy Robinson is endorsing Boris Johnson for prime minister. And the Labour party is way off on the far left.”

Berry, who earlier on Tuesday launched the Green party manifesto with a pledge to eliminate net carbon emissions by 2030, said she was shocked that discussion of the climate emergency between Johnson and Corbyn was so brief.

Asked who she trusted more on the environment, Berry said: “It’s impossible to tell from that debate because the question about climate chaos was relegated to a ‘quickfire’ section. I can’t believe that neither of those two leaders brought up the most important issue that we face, alongside Brexit. It’s outrageous. The young people that are out on the streets literally begging us to do something about this must be feeling so let down.”

Sturgeon, the SNP leader, when asked why her party should be supported, replied: “People in Scotland should vote SNP firstly to deprive Boris Johnson of the majority he craves, to make sure he doesn’t have a free hand to do what he wants to do.”

While Corbyn had used the main debate to insist Labour, if backed in government by the SNP, would not allow an immediate Scottish independence referendum, Sturgeon said all would be up for discussion.

“I drive a hard bargain and, first and foremost, I would want to make sure that Scotland’s voice and Scotland’s interests were heard and protected in a way that they simply haven’t been at Westminster over these past few years,” she said.

Farage, the Brexit party leader, who is not standing for parliament and who has withdrawn about half his candidates, said one non-Brexit policy his party sought was more direct democracy.

“If people want referendums, they should have the right to call them,” he said. On what would be asked, he said: “It’s not for me to decide, it’s for people to decide. I’m suggesting that if 15% to 20% of the electorate signed a petition to say ‘we want to have a say on this issue’, they should be able to do so.”

Asked later what he, personally, did to protect the environment, Farage conceded he could not name a single thing: “I drive all over country, I catch a lot of aeroplanes every year, I am not a leading example,” he admitted.