The format had been agreed months ago and National would not agree to any extension of the format, which was for a 30 minute debate between Prime Minister John Key and Labour leader David Cunliffe, moderated by Mike Hosking.
''I was surprised TVNZ only asked for 30 minutes but all the debates are agreed six to eight weeks out and that's it.
''Planning meetings are held, the channels come with their ideas on segments, where and when and the candidates. We never change.''
TV3 wanted to change the format of its leader's debate and National said no because of the previous agreement, Mr Joyce said while in Dunedin yesterday.
Mr Cunliffe said the issues raised in Monday's Moment of Truth, organised by Kim Dotcom, about spying in the country meant the TVNZ debate must be extended.
New Zealanders deserved answers and they needed them before the election.
''They will not get them from John Key's evasive answers on the campaign,'' he said.
Mr Cunliffe said last week he did not want the last few days of the campaign dominated by debates about spying and the role of the Government Communications and Security Bureau, but appeared to have changed his mind yesterday.
