The BBC had said it will not include the Green party in next year’s proposed 2015 General Election TV leader debates, rejecting demands that the party should receive the same coverage as Ukip.

The broadcaster argued that Ukip has seen a substantial increase in support unlike the Greens.

But the Green party responded by accusing the BBC of concentrating too much on its past performance.

Earlier this month, the BBC, ITV, Sky and Channel 4 announced joint plans to hold three debates in the six weeks before polling day. One would be a head-to-head between Mr Cameron and Mr Miliband. The second would involve these two leaders and Nick Clegg, while the third would also include Mr Farage.

As it emerged that the Green party faced exclusion, almost 200,000 people signed an online petition calling for the party to received equal coverage to Ukip as both have an MP.

In pictures: The rise of Ukip Show all 8 1 /8 In pictures: The rise of Ukip In pictures: The rise of Ukip 1993: Alan Sked forms Ukip History professor Alan Sked had been active in anti-EU politics for a while beore he founded Ukip in 1993. He resigned from the party after the 1997 election, concerned that it was attracting far-right members, and has been critical of Ukip since. Picture: Reuters Reuters In pictures: The rise of Ukip 2005: Kilroy defects Former TV presenter Robert Kilroy-Silk founded Veritas in 2005, after a failed bid to become leader, and took many of Ukip's elected members with him. But the party slowly lost its popularity and didn't put forward any candidates in the last election. Picture: REUTERS/Kieran Doherty REUTERS KD/RUS In pictures: The rise of Ukip 2010: Farage becomes leader, again Farage had led Ukip from 2006 until 2009, when he stood down to fight against the Speaker, John Bercow, for his Buckingham seat. He failed to win the election and returned to lead the party in November 2010. Picture: REUTERS/Kieran Doherty REUTERS/Kieran Doherty In pictures: The rise of Ukip 2010: Ukip fights for election Nigel Farage was injured in a plane crash on polling day in the 2010 general election, but his party increased its success in the votes. It fielded 572 candidates and took 3.1% of the vote, though failed to win any seats. REUTERS/Darren Staples REUTERS/Darren Staples In pictures: The rise of Ukip 2013: Eastleigh gains Ukip's candidate Diane James got the highest ever number of votes for any candidate from the party, but was beaten by the Liberal Democrats. The surge in support gave Ukip confidence ahead of local and European elections later in the year. Picture: Reuters In pictures: The rise of Ukip 2013: Bloom kicked out Godfrey Bloom, who served as an Ukip MEP from 2004 to 2014, had the whip withdrawn in 2013 after sexist comments and an attack on a journalist. He sat as an independent MEP until 2014, when he ended his term in office. Picture: REUTERS/Luke MacGregor In pictures: The rise of Ukip 2014: European election success Ukip got a higher proportion of the vote than any other party in 2014's European elections, adding 11 new MEPs and taking its total to 24. REUTERS/Luke MacGregor In pictures: The rise of Ukip 2014: Carswell defects Douglas Carswell defected from Ukip at the end of August, and was followed by Mark Reckless at the end of September, who resigned from the Tories amid rumours of many more defections to come. Picture: REUTERS/Toby Melville

In a letter to the Green party’s director of communications seen by the Guardian, the BBC said: “Ukip has demonstrated a substantial increase in electoral support since 2014 across a range of elections” supported by a robust trend across a range of opinion polls.

“The Green party has not demonstrated any comparable increase in support in either elections or opinion polls,” the letter went on. Addressing successful Green performances in elections at the expense of the Liberal Democrats, the BBC argued the shift “has been mainly the result of the decrease in support for the latter as opposed to a significant increase in support for the Green party”.

It added that opinion polls do not yet show that the Greens are currently at a level pegging with Nick Clegg’s party.

“Even if they did, we would still, of course, be taking as our starting point the result of the 2010 general election, where the Lib Dems took more than 50 seats and 23% share of the vote, demonstrating a level of electoral support overall substantially ahead of the Green party,” the letter continued.

The broadcaster added that it will “keep any new evidence of increased support for the Green party under close review” and said that if the debates are successful it would consider “offering appropriate opportunities to other political parties” in line with its obligation to be impartial.

In a response seen by the Guardian, Green party leader Natalie Bennett criticised the BBC for concentrating on its past performance rather than looking at current polling data for the Greens and the Liberal Democrats.

Bennett cites a piece by leading pollster Peter Kellner which describes how the Greens are closing in on the Liberal Democrats as painting a realistic picture of where the Greens are in the political landscape, and said the party is concerned that the BBC is basing the debates on the results of the 2010 General Election.

“This demonstrates very clearly how the BBC appears to be acting as a worrying brake on democratic change; I believe they are failing to grasp that the future of politics doesn’t look like the past,” she said.

She added that “more people are recognising every day that the business as usual approach to economics, society, environment and politics is now untenable.