The sister of Tory Brexiteer Jacob Rees-Mogg is to stand as a candidate for Nigel Farage's new Brexit party in the forthcoming European elections.
Annunziata Rees-Mogg was introduced by the former UKIP leader at the party's campaign launch at a factory in Coventry.
Addressing cheering supporters, Ms Rees-Mogg said it was not a decision she had taken lightly after years loyally supporting the Tories.
"I joined the Conservative Party in 1984 and this is not a decision I have made lightly - to leave a party for which I have fought at every election since 1987, from Maggie Thatcher through to Theresa May.
"I know which one I'd rather have representing us now."
She added: "The point at which our prime minister will not listen, not only to her membership, but will not listen to the people of her country... I can't sit by and let her do it.
"We've got to rescue our democracy, we have got to show that the people of this country have a say in how we are run.
"That the politicians are not our masters - they are to do our bidding."
Ms Rees-Mogg twice stood unsuccessfully as a Conservative general election candidate.
Mr Farage said that "thousands" had applied to stand in future local and Westminster elections and 70 had been selected to fight the European Parliament polls on May 23.
He told supporters that donations of more than £750,000 to the Brexit party within 10 days showed that small donors were funding a "rebirth of democracy in this country".
He said he did not know how the Brexit party would do, but had placed a £1,000 bet at 3-1 on it topping the polls in the European elections.