Reform UK has hit 230,000 members in a milestone for Nigel Farage's party.
It comes after the party gained more than 600 seats and took control of 10 local authorities in last week's local elections.
Reform also gained their first female MP, after Sarah Pochin won the Runcorn and Helsby by-election by just six votes.
The party picked up control of councils across the country, including Staffordshire, County Durham and Cornwall.
Nigel Farage celebrating
PA/X
Reacting to today's news, a Reform spokesman said: "Reform has all the momentum in British politics and we are continuing to grow every day."
Other parties have spent the weekend scrambling to react to Reform's success. Conservative co-chairman Nigel Huddleston sought to play down the threat from Reform UK, telling Sky News: "When they’re in a position of delivering things, that’s when the shine comes off."
Liberal Democrat leader Sir Ed Davey said Labour and the Tories had both made a "mistake" in their handling of Reform UK.
He added: "The Conservatives have been copying Reform policies, Labour is sounding more and more like Reform...I think the way you defeat NigelFarage is by calling him out."
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Nigel Farage and Sarah Pochin spoke to the media after Reform UK's victory PAHealth Secretary Wes Streeting called Reform UK "a real threat" saying the party was a "serious opposition force."
He continued: "It’s not yet clear whether at the next general election it will be Reform or the Conservatives that are Labour’s main challenges, but we’ve got to take that threat seriously."
Green Party co-Leader Carla Denyer MP said: "We have taken seats off the Tories and Labour and have shown we can be the positive and progressive antidote to Reform, holding their vote back in some places while breaking through onto other councils where Reform dominated."
Pollsters have warned the results could prove positive for the SNP in Scotland, with Sir John Curtice saying there is “no reason to disbelieve" the message from opinion polls about Reform’s level of support.
Sir John Curtice
GB NewsHe said that while Reform is not polling as high in Scotland as it is south of the border, relatively few people are switching their votes from the SNP to Farage’s party.
"I think the message from down south on Thursday is bad news for Anas Sarwar. It’s bad news for the Scottish Conservatives," he told BBC.
"And it is good news for John Swinney, not because it indicates that the SNP are going to ride high in the polls.
"It’s simply that he probably doesn’t have to do an awful lot better than the SNP did last summer – but that, given the way the Holyrood electoral system works, probably means that the SNP would pick up the vast bulk of the first-past-the-post seats.
"That would not be sufficient to give the SNP a majority or anything like it, but certainly would ensure the SNP is still the dominant party in the next Scottish Parliament."
