On Thursday morning Green Party sources said it had 43,829 members as of midday. Ukip's reported membership is 41,966.
Green Party sources also claimed to have put on 2,000 members yesterday, in what potentially is its biggest one-day surge in numbers ever.
At the time of publication the Greens said they had 35,481 members in England and Wales, 8,026 members in Scotland and 322 in Northern Ireland.
The Green Party currently has one MP, Brighton Pavillion's Caroline Lucas. It will hope to cling on to that seat in 2015 and possibly add another in Bristol.
Ukip currently has two MPs, Tory defectors Douglas Carswell and Mark Reckless. Nigel Farage hopes to get at least a handful more in May.
The figures come as the party battles to get its leader, Natalie Bennett, into the televised general election debates. The Green Party's lobbying effort with the broadcasters was made harder after Ofcom ruled it was not a "major party" in the same way Labour, the Tories, the Lib Dems and Ukip are.
A spokesman for the party told HuffPost its membership figures and latest polling "further calls into Ofcom's initial view that the green party is not a 'major party'."
David Cameron has said he will refuse to take part in the debates if the Greens are not involved. However the other party leaders have accused him of using that as an excuse in an attempt to run away from the debates.
This morning Nick Clegg said the idea the prime minister really cared about Bennett being allowed onto the stage was "laughable".
This morning George Osborne insisted Cameron was "up for" televised general election debates - but only if the format is right.