The National Party's lost faith in Parliament's Speaker of the House, after revelations more than $330,000 tax-payer dollars were spent on his legal bill.

It follows defamation action brought by a sacked Parliamentary staffer who Speaker Trevor Mallard wrongly labelled a rapist.

Political editor Barry Soper says it's the biggest travesty he's seen during his time in Parliament.

Soper says Mallard was pinned into a corner when National demanded to know the cost.

He says the National Party will put up a vote of no confidence next year.

"Can you imagine Labour having to defend and support a man like Trevor Mallard?

"This is the party that preaches well-being and kindness. How can Labour support somebody like Trevor Mallard, who has put an innocent man through all this."

LISTEN ABOVE

• Barry Soper: Trevor Mallard should resign for his disgraceful behaviour
• Heather du Plessis-Allan: Trevor Mallard should never have been appointed as Speaker
• 'He needs to go' - Judith Collins on under-fire Trevor Mallard
• David Seymour condemns Trevor Mallard for wrongly calling staff member a rapist
• Bryce Edwards: Trevor Mallard doesn't have the right attributes for Speaker role