Figures suggest trend away from mainstream politics and put Greens only just behind the Liberal Democrats

Membership of the Green party of England and Wales has doubled since January this year to reach 27,618.

Ukip has seen its membership rise to 40,000 in October; close to that of the Liberal Democrats, suggesting a trend away from mainstream Westminster parties to smaller parties.

Both Ukip and to a lesser extent the Greens have been given a fillip by increasing publicity, including over how they should feature on TV in the coming election debates.

Facebook Twitter Pinterest Nigel Farage is interviewed at his party’s office in Kent. Photograph: Facundo Arrizabalaga/EPA

The Greens said they had recruited an extra 500 members – powered partly by Natalie Bennett, leader of the Green party of England and Wales, putting on a strong performance on BBC Radio 4’s Any Questions.

The party is polling about 6 to 7% in latest polls, just behind the Liberal Democrats.

A Green party spokesman said the party was committed to standing in at least 75% of constituencies in the 2015 general election – meaning 50% more people will have the opportunity to vote Green in 2015 than did in 2010.

Nearly half of the Green party membership is aged under 40 and more than 50% of the growth in membership this year took place in October and November, possibly a spillover from the Scottish referendum or a response to the publicity the party has received as a result of being excluded by broadcasters from the TV leaders’ debates.

Although its largest membership areas are in the south and south-west, the party’s largest percentage rise this year has occurred in the north-west, Yorkshire and Wales, suggesting it is putting down stronger regional roots.

The Scottish Greens also increased its membership to over 5,000, more than doubling its previous numbers.

Labour insists its membership is stable, but has conceded it has a job on its hands to ensure the Green surge does not split the vote on the left allowing the Conservatives to hold seats they would otherwise have lost.

Bennett said: “This is a real landmark in the Green surge. To have doubled the membership of the party in less than a year is a real marker of the way in which people in England and Wales are seeing that we need real change in our society, not the business-as-usual politics offered by the three largest parties.

“Talking to new members around the country, their reasons, and the trajectories that brought them to the Green party, vary a great deal. There are many former Labour and Lib Dem members who are fed up with parties that are happy to see society continued to be run for the benefit of the 1% and the continued trashing of our natural environment. Others are former non-voters, who see that to create the rapid change we need we need a new kind of politics. Some are former Tories, horrified by the government’s fracking fantasy or worried by its failure to tackle our fraud-ridden, corrupt, reckless financial sector.

“These new members are putting their grassroots efforts and their financial support, as are many other supporters around the country, into making the 2015 general election transformatory. They understand there is a unique opportunity for a peaceful revolution delivered by enthused, energised voters.”

All political parties tend to experience an increase in membership ahead of an election, and then subside in the intervening years, but the Greens appear to be achieving a kind of breakthrough.

The party has been waging a long battle to persuade the broadcasters to allow the Greens into the election TV debates alongside Ukip and the other Westminster parties.