Gina Miller, the London investment manager and prominent pro- European Union campaigner, said on Wednesday she would use 300,000 pounds to encourage Britons to vote tactically for candidates in the upcoming election who opposed a "hard Brexit".
Miller, who in January won a Supreme Court case forcing the government to seek parliamentary approval before triggering Brexit, said Prime Minister Theresa May seemed set on a "hard Brexit" and that financial markets were wrong in presuming that the poll would see her soften her stance.
Last week Miller launched the "Best for Britain" campaign to raise money to back candidates in the snap election on June 8 who promised to hold a meaningful vote on May's final deal with the EU after two-years of divorce talks.
In six days, it has raised almost 300,000 pounds and this will be used to support candidates, inform voters, and ensure the "very best technology" to spread the message in areas where tactical voting could affect the result.
"We will work tirelessly to support candidates who want what's best for Britain and to keep all options open," said Miller, who ruled out standing for election herself.
Eloise Todd, the chief executive of Best for Britain, said polls suggested there were about 100 of the 650 seats up for grabs in parliament which were marginal and the result could be influenced.
Polling experts, however, are skeptical about how much influence tactical voting can have.
May, who has promised lawmakers will have their say on the final Brexit deal, has already ruled out seeking membership of the European single market and said she will seek to impose limits on EU immigration.
She has also warned that she would be prepared to walk away from talks without a deal rather than accept a bad one.
Her surprise snap election call led to a jump in sterling. Investors expect May to win a comfortable victory that will strengthen her hands in divorce talks and when dealing with those in her Conservative Party pushing for a "hard Brexit".
"It's a very strange reaction from the markets because I would say the opposite - it seems to be pointing that she's determined to do a hard Brexit," Miller told Reuters.
Miller's campaign is not the only one urging voters to oppose "hard Brexit" supporters. Open Britain, which campaigned for Britain to stay in the EU, has promised to target seats held by lawmakers, mostly from May's Conservative Party, who backed Brexit but where local voters did not.
Open Britain has already run into problems after three of its prominent Conservative members pulled out because of the campaign for tactical voting.
Miller, who received a torrent of online abuse during her legal challenge, said the intimidation had not stopped.
"I still have the same levels of threats, I still don't use public transport," she said. "It actually makes me fight even stronger because that is simply not a Britain I think should be allowed to develop."
(Editing by Guy Faulconbridge and Richard Lough)