Chuka Umunna has told ITV News he will take the battle to stop Brexit "to Boris Johnson's doorstep" at the next election after announcing he is switching to fight for the Tories' flagship central London seat.
Speaking to ITV News Political Correspondent Paul Brand on his Acting Prime Minister podcast, the Streatham MP confirmed it was his decision to stand for the Liberal Democrats against Tory MP Mark Field in The Cities of London & Westminster if and when a national vote is called.
The seat, which is currently held by Mr Field with a 3,148 majority, is one of the most iconic in the country and encompasses 10 Downing Street, Buckingham Palace, the City and the West End.
Mr Umunna, 40, also denied he was making an "opportunist" move by leaving a constituency he has held since 2010 but always won on a Labour ticket.
The former Labour MP, who in June joined the Liberal Democrats after leaving the hastily formed Change UK, told Acting Prime Minister: "I'm going to be standing in The Cities of London & Westminster. I've been appointed as the candidate there. This is a huge battle and highly symbolic.
"This part of central London ... not only is it a strongly Remain community. I know it well, I've worked here for the best part of a decade for businesses. Almost all my clients were in this constituency.
"I can see just how devastating leaving the European Union is going to be for so many of these businesses."
He added: "It really is taking it to Boris Johnson's doorstep. He currently lives in Downing Street and Number 10.
"On current polling it is an absolutely two-horse race between us and the Tories here and we're going to go for it."
Mr Umunna rejected the claim put to him by Brand that switching seats in London could be seen as opportunistic.
"Let's just look at the evidence right. Based on history you don't leave one of the two main parties if you are looking to be opportunistic," he said.
"I'm not coming into a Liberal Democrat safe seat. I'm coming into fight a seat where we are challenging the Tories.
"I'm not sure this 'opportunism' label based on the evidence is well made."
When it was suggested that he only switched because he wouldn't be able to win against Labour in Streatham, he said: "(I) completely disagree."
He added: "We've got a fantastic candidate ... The issue in Streatham is going to be who can you trust to promote the Remain cause. It scored the highest Remain vote in the country."
Acting Prime Minister has put guests ranging from Jacob Rees-Mogg and Jess Phillips to Ben Fogle and Bobby Norris in power and asked the question: "What would you do now?"
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Catch up with past episodes of Acting Prime Minister:
- Mark Francois on losing his dad and his pre-Brexit epiphany
- Anna Soubry opens up on pain of Umunna split and why Boris 'isn't fit to clean loos'
- 'Boris Johnson should have backed up ambassador' says Nicky Morgan as Acting PM
- Stella Creasy overhauls 'Hogwarts gone wrong' Parliament and ditches manifestos
- Labour's David Lammy justifies comparing Tory Brexiters to Nazis and defends Comic Relief 'white saviours' criticism
- Justine Greening on her bid to be Tory leader and calling Mark Zuckerberg
- Jacob Rees-Mogg backs Boris Johnson while outlining his own vision for the nation
- Why Ben Fogle would scrap exams and reintroduce national service
- Heidi Allen is 'too emotional' to be PM but wants Nick Clegg on her team
- Campaigning mum Hannah Deacon tackles medicinal cannabis in Number 10
- Sarah Champion on prostitution, pushing the nuclear button and Tinder dating
- Ben Bradley on exam obsession, getting kicked out of school and forgiving his digital past