New Zealand First leader Winston Peters has pulled out of tonight's minor parties debate, saying if Labour and National see no value in attending, neither does he.

"I cleared my programme and accepted that invitation enthusiastically," he said.

"Hence, I was astonished, on a general inquiry late Tuesday, to be told by them that neither Labour nor National had ever accepted the invitation."

Newshub political reporter Jenna Lynch told The AM Show she was surprised Mr Peters assumed Bill English and Jacinda Ardern would be taking part, as it's a minor leaders' debate.

"You have to sort of question things if he didn't realise that."

The Opportunities Party (TOP) leader Gareth Morgan also won't be taking part - but not by his own choice. He was excluded from the debate by TVNZ, who say he didn't make the 3 percent threshold needed to be invited.

Dr Morgan took TVNZ to court on Thursday in a bid to have its decision not to invite TOP reversed. He failed, with Justice Geoffrey Venning saying it hadn't been proved that TVNZ's criteria for participation were unfair.

Dr Morgan said he was naturally disappointed.

"The TVNZ minor leaders' debate now becomes a farce with the third, fourth and sixth ranking parties appearing alongside a man no one knows from a party that doesn't even register," he said.

Host Mike Hosking will also be absent, due to sickness. He will be replaced by political editor Corin Dann.

The Greens, the Māori Party and ACT are all confirmed participants for Friday night's debate, as well as United Future's newly appointed leader, Damian Light.

Newshub.