Labour Party front-bencher Grant Robertson has made fun of the National Party leadership contest.

He has slammed Finance Minister Bill English in Parliament, saying he's boring his way to glory.

"His campaign is sponsored by Mogadon - New Zealanders are going to sleep."

LISTEN: Bill English: 'Don't expect any policy U-turns if I'm PM'

Mr Robertson also had some words for Health Minister Jonathan Coleman, suggesting the soundings he has taken on becoming National's next leader were taken in his bathroom mirror.

"As he is known to most New Zealanders - who? Or, cheerfully, Doctor Who."

And the Labour MP has also given Judith Collins a serve saying she doesn't bear grudges, rather she embraces them.

"Keeps them in a locked, dark cupboard, nurtures them into full-grown feuds, and then unleashes them onto Cameron Slater for safe keeping."

WATCH: Judith Collins: No tax cuts if I'm PM