As the row over the general election debates puts it in the political spotlight, the Green Party gains more than 2,000 new members in the last day alone, overtaking both Ukip and LibDems.
A spokesman said the party now has 44,713 members, ahead of both Ukip’s membership of 41,943 and the Lib Dems, who have 44,526 people on the books, according to the latest figures from November.
Prime Minister David Cameron says he will not participate in a debate without the Green Party if Ukip are given a place alongside the leaders of the Conservatives, Labour and the Lib Dems.
Ofcom has ruled that the Greens should not be considered a major party for the purposes of campaign coverage, but decided that Ukip should.
Read more - FactCheck: is Ukip a 'major party'?
Green Party leader Natalie Bennett has written to Ed Miliband, Mr Clegg and Nigel Farage calling on them to allow the debates to go ahead by accepting her involvement.
— Green Party Memes (@GreenPartyMemes) January 15, 2015
Green Party system is crashing due to high demand from new joiners, we expect to overtake the Lib Dems today if it holds up #GreenSurge
— Tom Chance (@tom_chance) January 15, 2015
At one stage on Thursday the new members page of the party’s website crashed.
In September, Labour had 190,000 members, ahead of the Tory membership of 149,800. Party membership figures are not independently monitored and some parties have reportedly left members on the books to bolster numbers.
In 2010, when the first televised debates took place, then prime minister Gordon Brown appeared alongside Mr Cameron and Nick Clegg.