LONDON (REUTERS) - Gina Miller, the London investment manager who led a successful legal challenge over the triggering of Britain's exit from the European Union, launched a crowfunding bid on Wednesday (April 19) to back opponents of a "hard Brexit" in the planned June election.

British Prime Minister Theresa May announced on Tuesday that she wanted to hold a snap election on June 8 which she hopes will give her a stronger personal mandate at home and in divorce talks with the EU leaders.

Miller, who in January won a Surpeme Court case to force the government to seek parliamentary approval before triggering Brexit, said her new "Best for Britain" campaign would raise money to support election candidates who promised to hold a full vote on May's final Brexit deal.

"How people decide to vote is vital," Miller said in a statement. "If the deal the next government negotiates doesn't match up to our current terms, MPs (members of parliament) should do what's best for Britain and reject it."

She said she wanted to instigate the "biggest tactical voting" effort in British history to prevent a "hard Brexit".

May, who has promised lawmakers would 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.

Miller's campaign is seeking to raise cash on crowdfunding websote GoFundMe and had raised 5,200 pounds (S$9,341) in its first 16 hours.