Luciana Berger claims her decision to leave the Labour Party earlier this year was in the "national interest".
Ms Berger, now a Liberal Democrat candidate, left Jeremy Corbyn's party in February over its handling of antisemitism allegations.
"I couldn't in any way, shape or form, do anything that was essentially saying vote for me and get Jeremy Corbyn as the Prime Minister, because I don't think he is fit to hold the highest office of our land," Ms Berger told talkRADIO's Julia Hartley-Brewer.
"I put my national interest first rather than party first."
Ms Berger founded the Independent Group for Change - also known as Change UK - after leaving Labour, before joining the Liberal Democrats in September.
She claimed that although Labour was in her "DNA", the party had evolved "for the worse".
"The Labour Party was part of my DNA, my family's heritage" she explained.
"But parties evolve more often than not. They should evolve for the better, but the Labour Party and Conservatives have evolved for the worse.
"We have to do things that challenge that, and that’s what I have done."
The Liberal Democrats launched their election campaign yesterday, with party leader Jo Swinson pledging to channel £50 billion into public services by keeping Britain in the EU.
The Conservative Party are set to launch their election campaign today, along with the Green Party.
The five-week general election campaign period officially begins today.
Parliament was dissolved shortly after midnight, meaning there are now no MPs.
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