Tim Farron is to take the so-called Liberal Democrat "fightback" to a trio of marginal constituencies and urge voters to elect MPs from his party to strike a blow to "Theresa May's hard Brexit agenda".
Mr Farron will be joined in three London seats by former cabinet ministers Sir Vince Cable and Sir Ed Davey, alongside the winner of the by-election which saw Zac Goldsmith ousted from the Commons, Sarah Olney.
He is likely to push the party's anti-hard Brexit agenda in Kingston and Surbiton, where former energy secretary Sir Ed is seeking to make a comeback and overturn the Tories' 2,834 majority.
Sutton and Cheam appears to have a more even split of Remain and Leave voters, but Mr Farron will visit in the hope that the Lib Dems can take back the seat it lost to the Tories in 2015, having previously held it since 1997.
The party leader will then take the fight to Labour in Hornsey and Wood Green, and could use the visit to reprise attacks on Jeremy Corbyn, given that it is held by his ally Catherine West.
Speaking on the first day of the Lib Dems' election battle bus tour, Mr Farron will say: "The Liberal Democrats are ready to paint swathes of London and the country yellow again.
"Britain needs a strong opposition with pro-European MPs like Ed Davey, Vince Cable and Sarah Olney who will hold this government account.
"Every Liberal Democrat MP elected is a blow to Theresa May's hard Brexit agenda.
"Millions of people across the country are deeply worried about the direction our country is heading in. This is their chance to change Britain's future and stop a disastrous hard Brexit."