A parliamentary sign language interpreter has been criticised for going on a bizarre, profane rant against several National Party MPs during Deputy Prime Minister Winston Peters’ post-budget address.

Deaf New Zealanders watching the speech were horrified as the interpreter apparently went way off script, forgoing addressing the budget in favour of berating, belittling and insulting opposition members.

The interpreter interspersed their abuse with a number of vulgarities, including “bollocks” and “rat’s derriere,” and repeatedly referred condescendingly to MPs as “sunshine.”

“I don’t know why the sign language interpreter would say these things,” remarked one viewer. “I wanted to hear what Winston had to say about the budget, but instead we got this somewhat unhinged rant full of mockery.”

Viewers said the off-topic rant began as soon as Peters began to speak, and the interpreter appeared to “get themselves back under control” once it was over.

“It was truly bizarre. They did all the other leaders’ speeches just fine.”

Parliamentary Services is investigating.