Former British foreign secretary Boris Johnson’s sister is to stand as a European election candidate for Change UK, the pro-Remain group set up by The Independent Group of MPs.
Rachel Johnson, who will stand in the South West region, announced her move at an event to launch the party's election campaign in Bristol.
She was joined on stage by former BBC Newsnight presenter Gavin Esler, who is also standing.
Mr Esler, who has more than 40 years' experience in journalism, said: "I have never been a member of a political party but I am now.
"I have never been a candidate in an election but I am now.
"I have never been seriously worried about the future of our country but I am now.
"Our political system is a joke. It is a worldwide joke.
"They are laughing at us - not with us, at us."
Change UK interim leader Heidi Allen told the event that 3,700 people had offered to stand as party candidates in the European elections.
"This is no rebel alliance - this is the home of the remain alliance," she said.
Separately, Brexit Party leader Nigel Farage has pledged to target Labour voters.
Speaking at a campaign event to announce five new candidates, he said the party was already "doing very well" with Conservative supporters.
The former Ukip leader said: "There are five million people that voted for Jeremy Corbyn and voted for Brexit as well and that's going to be our task.
"I think we will go on squeezing the Conservatives and squeezing Ukip down to virtually nothing.
"We're going to go after that Labour vote in a very big way."