We would not be fulfilling our obligations of impartiality to the voters of Northern Ireland if we were to invite one of the Northern Ireland parties but not all the others, which also have substantial support in Northern Ireland.

In separate letters, ITV and the BBC have written to Peter Robinson and set out the reasons for not including the DUP in either network debate. Both the BBC and UTV plan dedicated debates in Northern Ireland involving all the larger Northern Ireland parties.

The BBC’s Director-General, Tony Hall, said: “We would not be fulfilling our obligations of impartiality to the voters of Northern Ireland if we were to invite one of the Northern Ireland parties but not all the others, which also have substantial support in Northern Ireland.”

An ITV spokesperson said: “We take the view that these proposals best meet the objective of delivering a series of relevant and valuable political debates for viewers across the UK. We are satisfied that it is in the public interest to proceed with these proposals as they now stand.”

The broadcasters point out that voters who live in Northern Ireland have a different set of choices from voters elsewhere. The five major parties in Northern Ireland are all different from those in the rest of the UK. In Northern Ireland the main parties are the DUP, Sinn Fein, the Ulster Unionist Party, the SDLP and the Alliance Party. BBC Northern Ireland and UTV plan debates involving those parties and all viewers in Northern Ireland will be able to see them.

If the DUP were included in the network debates it would be necessary to include all the other major Northern Ireland parties too. Including only one, or some, of the Northern Ireland parties would be unfair and discriminatory to the rest. Including all the major Northern Ireland parties in the network programmes would mean having 12 participants - and 97 per cent of viewers, in the rest of the UK, would not be able to vote for at least five of those 12 parties. The broadcasters say that such an arrangement would be disproportionate and not in the wider interests of viewers throughout the UK.

The proposed structure of the debates is fair to all voters, letting everyone see the leaders of the major parties they can vote for:

In the network debates all voters in England, Wales and Scotland will be able to see all the main choices available to them on election day.

In the Northern Ireland debates all voters in Northern Ireland will be able to see all the main and different choices available to them on election day.

The broadcasters today reiterated that the network debates will go ahead even if any of the invited leaders decline to participate.

The broadcasters said: “We are proposing that the debates should happen within the campaign period at a time when the parties will be setting out policies in their manifestos and when the audience is fully engaged with the election. The 2015 campaign will be nearly six weeks long and there is plenty of time for three debates to be held without overshadowing the rest of the campaign.”

“The proposed dates for the network debates are 2, 16 and 30 April. The order of the debates is to be discussed with the parties. In the event that any of the invited party leaders decline to participate, debates will take place with the party leaders who accept the invitation.”

JH