Party writes to broadcasters seeking an explanation within two days and a meeting within a fortnight where it can make its case

The Green party has written to broadcasters warning that unless it is given an explanation within two days for its planned exclusion from the general election TV debates it will have no alternative but to start a formal legal process.

The party also demanded a meeting with the broadcasters within a fortnight where it will seek to explain why it believes the exclusion is unfair.

On Monday the broadcasters – the BBC, ITV, Channel 4 and Sky – set out a complex schedule for the TV debates that would allow Ukip to participate in one of three proposed programmes, and the Liberal Democrats in two.

David Cameron and Labour’s Ed Balls have both said they can understand why the Green party feels aggrieved by the decision, and nearly 150,000 people have signed a Change.org petition calling for the Greens to be included.

The Green party’s letter says: “Since the announcement we have been inundated with calls to the office from the public expressing disbelief at your decision. Online petitions have been started and they are attracting tens of thousands of signatures.

“Political commentators have declared the decision to be unfair and even the prime minister has called for the Greens to be included in the debates on the grounds of fairness. We would like to be informed on how the decision was made and what criteria you took into account when reaching your conclusions.”

The letter from Penny Kemp, the party’s head of media, who is taking a lead on the issue, adds: “The Green party received 150,000 more votes than the Liberal Democrats in the 2014 European elections and won three times as many seats as them. In general election opinion polls the Greens are neck-and-neck with the junior coalition partners.

“Despite our comparative lack of airtime, our policies are consistently popular with the public. We have a 5% lead over second-placed Labour when people vote for policies; 64% of the public back our plan to turn the minimum wage into a living wage, and 66% support building more social housing.”