UK PM May has weakened her Brexit hand by calling snap election: Gina Miller

Key Points
  • Pro-EU campaigner Gina Miller has launched Best for Britain, a tactical voting campaign to "stop Extreme Brexit"
  • Miller told CNBC's Squawk Box that she is "trying to give people the choice"
  • Best for Britain has raised over £300,000 through crowdfunding, Richard Branson is reported to have donated £25,000

U.K. Prime Minister Theresa May's decision to call a snap election on June 8 could spell disaster for the country's looming divorce talks with the European Union, argued one of the Brexit debate's key voices on CNBC's Squawk Box Thursday.

"By calling this election (Theresa May is) going to put in her manifesto exactly what her approach to Brexit is going to be," pro-EU campaigner Gina Miller said. Miller is also the co-founder of investment firm SCM Private. "She's going to show all of her hand," Miller reasoned, deeming the surprise vote announced last week "ludicrous."

Miller was on Squawk Box following the launch Wednesday of her latest Brexit-related campaign, Best for Britain, which advocates tactical voting in order to "stop Extreme Brexit," according to its crowdfunding page.

When asked if she was trying to prevent Brexit, Miller explained that she is only trying to give people the choice. "If the only deals on the table are a bad deal or a no deal, that's not a real choice," she said.

A bad deal or no deal shouldn't be the only Brexit options: Gina Miller

According to Miller, MPs should be allowed to vote on an EU trading relationship which could end up in three scenarios: a "fantastic deal," World Trade Organisation rules or a bad deal for the U.K. Miller highlighted the option of staying in the bloc as a fourth scenario. "That is the only way that MPs get a meaningful vote," she said.

The Best for Britain campaign will look at places where candidates in favor of choosing from an array of options on Brexit stand a good chance of winning a seat. Miller said that, "It's not against Brexit. It's about ensuring that the process is one that's transparent and democratic because if we have a huge landslide like some people are predicting, then the government can basically do whatever they want."

UK PM May has weakened Brexit negotiating position by calling election: Gina Miller

Miller, a Labour supporter, spoke of her anger at the party's perceived troubles, saying that they were in "disarray." "If the opposition are not going to do their job and stand up to government, then we've got to encourage other people to do that," she argued.

She clarified that Best for Britain was not about picking a particular party, it was about "identifying" candidates. It also aims to encourage young people to vote.

Miller said that her intention was to "narrow (a) Conservative victory," as she could not see the Tories losing.

Snap election makes 'Hard Brexit' less likely: Absolute Strategy

By contrast, Richard Mylles, political analyst at Absolute Strategy Research, told CNBC's Street Signs Thursday that May would "increase her authority" post-election. He reasoned that May's expected electoral mandate would keep Eurosceptics within her own party in line.

Miller said that she did not want to stand as an MP as she was focussed on her investment career and charity work.

A YouGov/Times survey published Thursday revealed that 45 percent of voters believe that opting to leave the EU was a mistake, while 43 percent backed the decision.

At the time of writing, Miller's crowdfunded campaign had raised £324,844. U.K.-based press have reported that Richard Branson, founder of the Virgin Group and remain supporter, donated £25,000 to Best for Britain.

Follow CNBC International on Twitter and Facebook.