Liberal Democrat leader Tim Farron chose Vauxhall to announce the party's membership had surged past 100,000.
The Lib Dems have welcomed more than 12,000 new members since Theresa May's decision to call a snap election.
And with George Turner's energetic campaign underway in Vauxhall to oust Brexit campaigner Kate Hoey, who is at odds with the 78% of the borough of Lambeth which voted to Remain, Tim joined a rally in the main hall at St Anne and All Saints to launch the constituency campaign and mark the membership milestone.
And Tim emphasised that a vote for Labour in Vauxhall would be a vote for UKIP.
He said: "One of the opposition parties over the weekend decided to back another of the opposition parties.
"You might have seen Paul Nuttall on the television on Sunday morning saying that UKIP's candidate here in Vauxhall is basically going to be Kate Hoey.
"The reality is that we have, if you like, a coalition of chaos - the Conservatives, Labour and UKIP all lined up backing the hardest of all Brexits, exit from the single market, cutting off all our ties with our friends and neighbours in Europe, despite those things never being on the ballot paper.
"We say the British people can choose a different future."