Gina Miller, the campaigner who defeated the government in the High Court over the triggering of Article 50, is launching a new initiative to oppose "extreme Brexit".
The 52-year-old investment manager will encourage voters to cross party lines and vote tactically on 8 June to elect MPs who will reject an EU deal which is not in Britain's interests.
She has set up a crowdfunding page to back the initiative, titled Best For Britain, which will pledge money behind a slate of candidates that align with the group's interests.
Introducing the campaign following Prime Minister Theresa May's shock snap election announcement, Miller said: "We are launching a tactical vote campaign, aiming to ensure the final vote on the Brexit deal is a real one; one that is best for Britain.
"We need to prevent MPs and the people being forced into an extreme Brexit that is not in Britain's best interests.
"We will support candidates who campaign for a real final vote on Brexit, including rejecting any deal that leaves Britain worse off."
The fund has raised over £70,000 in donations since launching on 18 April.
Its most likely recipients will be Labour and Liberal Democrat candidates, although Miller has not ruled out helping independents and even Conservative candidates who will oppose the government on an unfavourable Brexit deal.
Bypassing party hierarchies
Miller told the Guardian she launched the campaign as a pragmatic way of supporting progressives, given the short amount of time before the election, and that she will bypass party hierarchies if necessary. "There isn't time to organise a formal progressive alliance," she said.
"We have to do what we can in the time available. We need to re-energise people about the importance of voting tactically."
She added: "We need to have a strategy and a structure. Time is not on our side, so we have to put aside egos. It is about being pragmatic."