However, both the Tories and Labour have ruled out the possibility of a referendum on the subject and time to change their minds is running out.
Sir Patrick told Sky News there is "no doubt" both Star Trek's Jean-Luc Picard and X-Men's Professor Charles Xavier would have backed staying in the European Union.
Hundreds of supporters of the campaign were at the rally in Camden, north London, to hear speeches from Sir Patrick, Ms Soubry, Mr Umunna, Lib Dem MP Layla Moran and Caroline Lucas, a co-leader of the Green Party. What the government comes back with, not what was promised in the referendum, will be the real deal.
The Individuals's Vote marketing campaign is demanding the British public be given the ultimate say on the deal secured by Prime Minister Theresa May, slightly than MPs in Parliament.
Speaking to the BBC at the event, Labour peer Lord Adonis said: "People want a say..."
"We'll do everything we can in Parliament for a people's vote".
During a speech to the crowd, Green Party MP Caroline Lucas will say: 'We will be making the case in Parliament, but this is too big and too important to be determined exclusively by politicians.
The British parliament's only Green MP, Caroline Lucas, said: "This is too big and too important to be determined exclusively by politicians".
Meanwhile, pro-Brexit demonstrators also turned up at the launch, and Conservative MP Nadine Dorries argued there was no public appetite for a second referendum.
Actor Patrick Stewart, a supporter of the People's Vote campaign, said campaigners were not asking for a second referendum, but rather wanted "another chance to consider what the terms of this divorce are going to be". "So the day we joined was one of the most exciting days of my adulthood", he added.
"I'm a war baby and growing up a lot of the world was not good".
"They voted with a substantial majority to leave the EU".
But he added: 'As time has gone by, the information that we are receiving about the terms and conditions of that separation are quite unlike the terms and conditions that were spoken of so loosely during the 2016 campaign'. Stewart had a role in Star Trek: The Next Generation.
Foreign Secretary Boris Johnson, who is steadfast in his belief that Britain can live long and prosper outside the European Union, riffed on another one of Star Trek's most famous lines in his response to Sir Patrick.