Prime Minister John Key walked across Parliament's debating chamber and shook David Cunliffe's hand to congratulate him on his election as Labour leader before the battle commenced.

Mr Cunliffe, with new deputy leader David Parker at his side, chose the complex issue of internet pricing and the Chorus company for his first clash.

Leadership rival Grant Robertson sat on the other side of Mr Cunliffe, in his new role as shadow leader of House, a position formerly held by Robertson supporter and America's Cup devotee Trevor Mallard.

Mr Cunliffe twice questioned Mr Key about getting a phone call from the chair of Chorus, but opened himself up to a right hook from Mr Key.


Perhaps with the memory of his first caucus meeting today fresh in his mind, he twice referred to Mr Key getting a call from the "chair of caucus".

On the third attempt, he got it right to mocking applause from the Government benches.

"One thing is true," said Mr Key, "I do get a phone call from my caucus, but they all voted for me.... I can only imagine what the phone call from Trevor is like in San Francisco at the moment.

Mr Robertson rose to his feet to criticise Speaker David Carter for not upbraiding the Prime Minister for his ''political slaps" at Mr Cunliffe.

"You have in the past said that is unacceptable and I would ask that you hold the Prime Minister to the standard that you have previously set," Mr Robertson protested.

Mr Cunliffe asked about 10 questions in all about the issue.

At the heart of is a dispute about how much the price of copper-based broadband should fall.

The Government opposes a Commerce Commission recommendation, which would be to the advantage of Chorus, an offshoot of Telecom and a listed company and a significant player in the roll-out of ultrafast broadband. Critics have estimated the advantage to Chorus would be $600 million, and are calling it a $600 million copper tax.

Blunders excepted, Mr Cunliffe was at ease with the subject as the former Communications Minister that split up Telecom.

At one point today he dispensed with his notes and questioned Mr Key directly on detail but he did not get the better of him.

At the end, he laid himself open to another right hook from Mr Key.

Cunliffe: "With [the Prime Minister's] reliance on reports, what reliance is he placing on media reports that this $600 million botch-up is the end of [Communications Minister] Amy Adams' chances of succeeding him and Prime Minister?"

Key: "I need to be honest. I really do not think our caucus is looking for a new leader right at the moment but after question time today the Labour Party [may well be]."