The Green Party is threatening legal action after the BBC rejected its bid to join a televised leaders’ debate during next year’s general election campaign.

Its move came as a YouGov poll placed the party in fourth place ahead of the Liberal Democrats.

The broadcaster justified the Greens’ exclusion on the grounds that unlike Ukip they had not demonstrated a big recent rise in support.

A petition calling for their leader, Natalie Bennett, to be included has been signed by nearly 200,000 people.

Penny Kemp, the party’s director of communications, said: “We have already met with our lawyers to discuss possible legal action but obviously we would wish to settle this by an amicable route and lines of communication are open with the broadcasters.

“We are meeting them in early November to discuss the leadership debates and at that meeting we will be reiterating why we should have a place at the table. This new opinion poll shows yet again that the Greens have a message that voters want to hear.”