The Liberal Democrats claim to have gained 1,000 members in the first hour after Theresa May called a snap general election for 8 June.
A press release from the anti-Brexit party claimed they had experienced a "surge" in membership applications on the morning of 18 June in the hour after May's announcement.
Lib Dem Leader Tim Farron was the first UK politician to respond to May's announcement, getting off the blocks within 15 minutes of her speech finishing.
He said: "If you want to avoid a disastrous hard Brexit. If you want to keep Britain in the single market. If you want a Britain that is open, tolerant and united, this is your chance. Only the Liberal Democrats can prevent a Conservative majority."
The Lib Dems have sought to position themselves as the real alternative to Brexit. Labour, the UK's main opposition party are battling with the dilemma posed by their supporter base being split over the issue.
The Lib Dems were reduced to eight MPs at the last election and received a smaller share of the votes than Ukip, who only managed to win one seat.
Prior to that routing, they had been the third largest party in the Commons, winning 57 seats in 2010.
The party have regained confidence since taking a single-issue approach to politics in the aftermath of Brexit.
They famously stunned former Mayoral candidate Zac Goldsmith in a Richmond Park by-election earlier this year; unseating the popular local MP with unknown candidate Sarah Olney by focusing solely on his stance on Brexit.
President of the Liberal Democrats, Sal Brinton, said: "This is a time when liberals must stand together, and people across the country are doing just that.
"The surge in our membership proves that the Liberal Democrats are seen as the real opposition to this Conservative Brexit Government.
"While Theresa May is seeking to divide the country, the Liberal Democrats are the only party fighting to keep Britain open, tolerant and united."