The anti-Brexit party Change UK has launched its European elections campaign, revealing a slate of 70 candidates that includes Boris Johnson’s sister, seasoned politicians disillusioned with their parties, and people completely new to politics.

Rachel Johnson said she was standing to make sure Brexit did not wreck the chances of a bright future for her children and other young people, and that her decision to stand was not an attack on her Brexiter brother.

Johnson, a writer and journalist who will stand in south-west England, did not speak from the stage at the launch event in Bristol but said afterwards: “I’m sure that Boris understands why this is not a vote against Boris. This is a vote for change. We need to move the dial. People need to have a say.”

However, Change UK ran into trouble only hours after the launch, when the party announced that one of its potential candidates, Ali Sadjady, had stood down having reflected on an “inappropriate tweet” posted in 2017. It had been reported that he had expressed support for Brexit because, he said, “70% of the pickpockets caught on the [London Underground] are Romanian”.

The new party has developed out of the band of MPs who broke away from their respective parties and formed the Independent Group at Westminster. Last week they created the new party, called Change UK: The Independent Group.

The group’s interim leader, Heidi Allen, told the launch event that 3,700 people from across the UK and from every background offered to stand to campaign for a “people’s vote” on Brexit.

Referring to the nickname for the group’s members and supporters, Allen called herself a proud “Tigger mum” and, with a nod to Star Wars, claimed: “This is no rebel alliance; this is the home of the remain alliance.”

Facebook Twitter Pinterest Gavin Esler, a candidate for Change UK. Photograph: Adrian Dennis/AFP/Getty

The first candidate she introduced was the former BBC correspondent Gavin Esler, who claimed Brexit was based on “cheating and lies” and said he was sick of the likes of Nigel Farage and Jacob Rees-Mogg peddling “snake oil”.

He added: “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.”

Victoria Groulef, a former Labour councillor in Buckinghamshire, said: “Last year it became clear to me that Labour was no longer my political home. In fact it’s a place I felt deeply uncomfortable and no longer valued.” She said she felt re-energised by the new party.

Andrea Cooper said she had no political background but was an “everyday woman from Liverpool” who worked with young people. “The main political parties are letting us down,” she said.

Other candidates include former politicians and activists, as well as teachers, nurses, carers, former members of the armed forces and citizens from other EU countries living in the UK.

Play Video 2:23 Change UK's Heidi Allen: 'This is the home of the remain alliance' – video

Change UK called on voters disillusioned with the chaos of Brexit and the politics of Farage and Ukip to vote for the party to send a strong message that a change in direction is wanted.

It said the individual stances of Labour or Tory MEPs who claimed to support a people’s vote were irrelevant because it was the party, not the individual, on the ballot paper. Change UK claimed every Labour or Tory MEP candidate was a sponsor of Jeremy Corbyn or Theresa May’s position on Brexit.

During a question and answer session, a member of the invited audience, Penny, from Bristol, said she wanted to hear more about the party’s other policies. She was told other policies would be announced soon.

The leading lights in the movement batted away suggestions that people may be confused by the array of parties with similar views that would be standing candidates in next month’s elections. The group’s Brexit spokesperson, Anna Soubry, said: “It’s very clear, this is the remain alliance. The Tiggers.”

The party chose the We the Curious science centre in Bristol for its launch, during which 50 candidates perched on a stage against a backdrop of posters featuring brightly coloured stripes. One observer described the scene as resembling a “trendy sweet shop”.

Facebook Twitter Pinterest Heidi Allen speaks at the launch. Photograph: Adrian Dennis/AFP/Getty Images

Asked what would be considered a good result, Chris Leslie, the party’s European election coordinator, said: “Our aim is to make sure the public have the choice to vote clearly and unequivocally to support a people’s vote.”