The four broadcasters behind plans for TV debates in the run up to the general election have threatened to empty chair David Cameron if he does not show up.
BBC, ITV, Sky and Channel 4 published the revised proposal after the prime minister said he would refuse to take part in the bouts unless the Green Party leader Natalie Bennett was also included alongside Nick Clegg, Nigel Farage and Ed Miliband.
Now the stations are offering one debate between the prime minister and the leader of the opposition and two debates involving the leaders of the Conservatives, Labour, Liberal Democrats, Ukip, the SNP, the Green Party and Plaid Cymru.
The broadcasters explained that the party leaders have been formally invited to take part in the debates and, if any decide not to participate, the debates would take place with those who accepted the invitation.
"BBC, ITV, Sky and Channel 4 remain committed to holding election debates in the General Election campaign," the broadcasters said in a joint statement.
"Following meetings with the Conservative, Labour, Liberal Democrat and Ukip representatives, it has not been possible to come to an agreement on the original proposal put forward by the broadcasters in October 2014.
"Since October the broadcasters have together and individually had a number of meetings and conversations with the parties invited to take part, the Conservatives, Labour, Liberal Democrats and UKIP, and also discussions and correspondence with the SNP, Plaid Cymru and the Green Party.
"All these discussions have been constructive and useful in informing our thinking about the debates.
"Over the three months since the original proposal was put forward, the broadcasters have also continued to monitor the electoral landscape, as we promised to do, taking into account the polling evidence, and the expressions of public support for the debates to go ahead and for a wider range of parties to be included in the debates.
"In view of these factors, the broadcasters are now inviting party leaders to take part in the following debates within the official election campaign and approximately two weeks apart."
The debates would take place during the general election campaign, with proposed dates of 2, 16 and 30 April.
One of the seven-party debates would be hosted by the BBC, the other hosted by ITV. The two-party debate would be hosted jointly by Channel 4 and Sky.