Tory activists have confirmed the date for an unprecedented new no-confidence vote against Theresa May .
The ballot of around 800 activists will be held on Saturday 15 June, local chiefs have been told.
The vote will not be binding, but activists believe it will pile pressure on the Prime Minister to quit.
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The vote will be held at an emergency meeting of the National Conservative Convention, the forum for senior Conservative activists across the country.
It was triggered after more than 65 chairmen and women of local Tory associations signed a petition demanding the summit.
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Theresa May is widely expected to lose the vote after wounding opinion polls found members want her gone.
A survey on Sunday found 82% of members want her out after losing 1,300 seats in a local elections drubbing.
The ballot will be the third no confidence vote Theresa May has faced since December - and the third type.
The first vote in December 2018 was a no confidence vote in her leadership by Tory MPs. She survived by 200 votes to 117.
The second in January 2019 was a no confidence vote in the Tory government by Labour . She survived by 325 votes to 306.
The third vote by grassroots activists will not be binding. Currently, she cannot face another binding vote - of the kind MPs held in December - until a year has elapsed since the last one.
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The vote will come just days after a State Visit to the UK by US President Donald Trump.
And it will happen just two weeks before newly-elected MEPs are due to take their seats in the European Parliament, despite original pledges that Brexit would happen in March.
Mrs May previously promised she would quit once MPs passed her Withdrawal Agreement - completing the first stage of the Brexit process.
Tories would then hold a full leadership election to decide who leads the second phase, around the future relationship.
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But several MPs and activists say she must go now.
Geoffrey Clifton-Brown, Treasurer of Tory MPs' 1922 Committee, said she must leave in the coming months - whether her Brexit deal is approved or not.
Leave-backers are furious with Mrs May's decision to delay Brexit to October 31 and enter 'soft deal' talks with Labour.
Those talks will continue today amid speculation the government is preparing to offer a temporary customs union lasting until 2022.
