The Green party has overtaken the Liberal Democrats in size after attracting thousands of new members this week.
The party claims it now has 44,713 members across England, Wales, and Scotland.
That is higher than the 44,680 total logged by the Lib Dems in their latest figures in April. And it is higher than UKIP's latest tally of 41,966 members.
It comes after a surge of 2,074 extra Green party members in England and Wales on Wednesday and 1,969 on Thursday. Both days are ahead of the previous best of around 750 new Green members added in one day, a party spokesman said.
Green party press officers said it was the busiest day for sign-ups on record:
More ppl joined @TheGreenParty yday than on any other day EVER. Fact. Please RT! #VoteGreen2015 #GreenSurge #InviteTheGreens @natalieben
The news will fuel the row over whether the Greens should be included in the pre-election TV debates. David Cameron has said he will not take part unless the party is invited – although critics say he is simply using that as an excuse to avoid the showdown.
The Scottish Greens now have 8,026 members, a party spokesman said. The SNP has around 93,000 members, after seeing a major surge from 25,000 following the Scottish referendum campaign last year.
Green leader Natalie Bennett said it was a major day for the party:
This second significant advance in a day reinforces the Green party's case to be included in the broadcasters' proposed Leaders' Debates.
At the May 2014 European Elections we saw three Green MEPs elected to the Lib Dem's one, we are polling level or above them with several pollsters, and now we have more members than them.
I offer my thanks to everyone who has joined us and help send a message to the broadcasters and the regulator Ofcom that the Greens' anti-austerity message – that we have to stop making the poor, the disadvantaged and the young pay for the errors of the bankers – must be heard.
A Lib Dem spokesman said:
"At the end of 2014 the party's membership was 44,680. This is an increase of 1,200 on the year before and means we have increased our membership for the second year in a row, and have increased our membership every quarter last year. During this time we became the first party in modern history to increase its membership whilst in government."