Exclusive: Sarah Wollaston becomes the second Conservative MP to officially join the campaign for another Brexit referendum.

Wollaston, the MP for Totnes, has signed up to the People's Vote campaign and is set to lead a rally for the cross-party group in Bristol later this month.

Anna Soubry was previously the only Conservative MP to officially support the campaign.

The People's Vote group is holding a "summer of action" nationwide as opinion polls suggest public support for another vote is on the rise.

LONDON — Sarah Wollaston has become the latest Conservative MP to officially join the leading campaign for a second Brexit referendum.

Wollaston, the Conservative MP for Totnes, confirmed to Business Insider she has signed up to the People's Vote campaign for a vote on the final Brexit deal, and is set to appear at a rally hosted by the group in Bristol on Saturday, August 11.

Wollaston, who also chairs the House of Commons Liaison Committee, is among a handful of Tory MPs who have publicly called for another nationwide vote on Brexit.

Justine Greening, ex-education secretary, came out in support of another referendum last month. Former ministers Anna Soubry and Philip Lee back a People's Vote, and Dominic Grieve has hinted at support for another referendum.

However, Wollaston is just the second Conservative MP to become an official supporter of the People's Vote campaign, which is pushing for a public vote on the terms of any Brexit deal Theresa May brings back to Westminster.

Wollaston's support for the campaign comes despite initially backing the campaign to leave the European Union, before switching sides in 2016, and despite saying earlier this year that campaigning for second referendum would risk damaging negotiations.

"We should not be talking about referendums or second referendums at this point," Wollaston told ITV in January.

"I think that trouble with saying that now is that it would just encourage the European Union to give us the worst possible deal."

Wollaston's latest shift follows the Electoral Commission finding that the official Leave campaign guilty of breaching spending rules.

Following their findings Wollaston told the House of Commons: "Consequences must follow, we cannot have confidence that this referendum was secure and it should be rerun." She has also tweeted support for another referendum on the UK's membership of the European Union.

She is now an on official part of the People's Vote movement — joining MPs like Labour's Chuka Umunna and Lib Dem leader Sir Vince Cable — and is set to play a headline role in the group's "summer of action" campaign.

Lib Dem MP Layla Moran, Labour's Chuka Umunna, and Green MP Caroline Lucas all back the People's Vote campaign. REUTERS/Simon Dawson

The "summer of action" will see the People's Vote campaign hold rallies in constituencies nationwide in the run-up to political party conference season, with confirmed locations including Edinburgh, Liverpool and Suffolk.

Wollaston is set to be a key speaker at the event in Colston Hall, Bristol on August 11. "We're expecting it to be a full house," a source close to the event told BI this week.

As BI reported last month, Wollaston's Conservative party colleagues Amber Rudd, Nicky Morgan and Antoinette Sandbach are also rumoured to be considering joining the People's Vote campaign.

Recent opinion polls suggest public support for another Brexit referendum with time running out in negotiations and the potential consequences of no deal becoming clearer.