UPDATE: On Thursday evening the Greens confirmed they now have more members than the Lib Dems, as well as Ukip (which had been announced earlier). They say 1,969 new members had joined today, bringing their grand total to 44,713.
Thursday afternoon: The Greens now have more members than Ukip after more than 2,000 people joined in less than 24 hours.
Their total of 43,829 is a combined figure bringing together all the members from the assorted Green parties in the UK - the Green Party of England and Wales (35,481 members), the Scottish Greens (8,026 members) and the Green Party in Northern Ireland (322 members).
Ofcom ruled last week that the Green Party was not deemed a "major party" in what was seen a blow to England and Wales leader Natalie Bennett's hopes of taking place in the televised leader debates in the build-up to the general election.
However, the latest figures add to growing evidence of support for the Greens. The party also announced last month that its membership figures had doubled in the space of a year.
The latest polling figures from YouGov, however, put the Greens on 7 per cent, lower than Ukip (15 per cent) but higher than the Lib Dems (6 per cent).