Former Labour MP Chuka Umunna will fight the Cities of London and Westminster parliamentary seat for the Lib Dems at the next general election.
Mr Umunna has represented the south London seat of Streatham since 2010.
But he has now been adopted as the Lib Dems’ candidate for the capital’s most central constituency, which includes London’s financial district.
The Lib Dems came third in 2017 with 4,270 votes. The Tories won with a 3,148 majority, with Labour in second.
The Conservatives have held the seat since its creation in 1950 but the Lib Dems are hopeful of a strong showing in an area which voted overwhelmingly to remain in the EU in the 2016 referendum.
In May’s European Parliament election, it is estimated that the Lib Dems won in the constituency by a clear margin.
Change UK founder
Former Foreign Office minister Mark Field, who has represented Cities of London and Westminster since 2001, is standing again for the Conservatives.
Mr Umunna helped found the Change UK party after he quit Labour in February.
But he left after its poor showing in the European Parliament elections and subsequently joined the Lib Dems – who are campaigning for the UK to stay in the EU.
Announcing the news of his target seat on Twitter, Mr Umunna said he “relished” the fight ahead.
The Cities of London and Westminster is a demographically diverse constituency which covers London’s West End, as well as the Palace of Westminster and Buckingham Palace.
Twice during the 1980s the Lib Dems came second to the Conservatives but the party has never received more than 21% of the vote and has often trailed behind Labour in third.
But the Lib Dems said the next election would be a “two-horse race” between them and the Conservatives and Mr Umunna was the “Remain choice”.
The Lib Dems have enjoyed a resurgence in the past year on the back of their anti-Brexit stance, coming second in the European elections and topping the polls in London.
On Friday, the party said its membership had risen to a record 120,845 figure.
