Labour smashed in latest poll (Fairfax Ipsos)

LATEST: Parker, Robertson back Cunliffe | Roy Morgan poll has Labour on 28%

Labour support has plummeted 6.3% to 23.2%, according to the latest Fairfax Ipsos poll. 

National climbs 8.9% to 56.1% — which would translate to 74 seats, easily enough to govern alone.

In the preferred prime minister stakes, John Key is up three points to 51.4%, Labour leader David Cunliffe down two to 11%..

The Fairfax Ipsos survey is the fourth post-budget poll to show National with strong support, and Labour knocked back.

The latest horror numbers arrive on the heels of the Mr Cunliffe embarrassment over a letter of support for Donghua Liu, and a day before a three-month pre-election window when Labour's caucus can change its leader by a simple majority vote (compared to the new primary system that saw Mr Cunliffe take control as votes from party members and affiliated unions outweighed those of MPs).

And while logic dicates that potential challengers like Grant Robertson and David Parker should bide their time, and let Mr Cunliffe take the rap for a likely dismal September 20 election result, NBR political editor Rob Hosking notes that logic often goes out the window in the heated environment of leadership stoushes — and that something seems to be afoot in the Labour camp (more from Mr Hosking shortly).

Mr Cunliffe has reportedly issued a warning to his colleagues overnight, saying members of caucus who move against him would be viewed like "scabs" (the derogatory term for workers who cross a picket line during a strike).

But some MPs could see themselves having nothing to lose. Political commentator  David Farrar notes that would translate to 29 seats, meaning if Labour holds 23 electorates it would have just six list MPs, putting the likes of Andrew Little and Jacinda Ardern under the gun, along with othe members of caucas — a pending outcome that could focus their minds in any leadership challenge.

Elsewhere in the Fairfax Ipsos poll, the Greens are down 0.8% to 11.9%.

NZ First falls 0.5% to 3.2%

Internet Mana is on 2.1%, enough to get three MPs into Parliament if Hone Harawira holds his Te Tai Tokerau seat, where he is polling behind Labour's Kelvin Davis.

ACT, United Future, the Conservative Party and the Maori Party all register below 1%.

The telephone poll surveyed 1014 people between June 14 and 17 and had a margin of error of 3.1%.