It’s been a long time between ACNielsen polls: the last one was at the beginning of December, just before Labor’s leadership change. It showed Labor with a huge lead, 56%-44% two-party-preferred.

Most of us dismissed this as unbelievable. Simon Jackman offered a detailed explanation of why it was “unrealistic”. But since then, other results have been in the same ballpark – Newspoll has said 55% or better three polls running – so election-watchers have been keen to see what Nielsen would say this time.

What it’s saying is Kevin Rudd’s best set of numbers yet. Labor is leading 58 to 42, a swing of more than 10% since the last election, off a primary vote of 46%. He also leads Howard for preferred prime minister, and has the highest approval rating (65%) Nielsen has ever recorded for an opposition leader in its 35 years of polling.

To appreciate the significance of this, some background is essential.

Prior to the last election, Newspoll consistently showed a stronger Labor than Nielsen did. (This was a blow to the cynics who thought proprietors dictated everything that went in newspapers, since Newspoll’s ultimate paymasters, News Ltd, were much more anti-Labor.)

Many observers just split the difference between the two and therefore expected a close election. Instead, Nielsen turned out to be almost spot on, and the Coalition won comfortably. That’s why Rudd will be more than usually pleased with today’s result.

Of course, a poll is not a prediction. No-one really thinks Labor will get a 10% swing. But it’s a big buffer to have against any government comeback. Nielsen’s John Stirton, as quoted in The Age, put it very well: “Kevin Rudd’s honeymoon with voters builds on Labor’s consistent lead established by Kim Beazley in 2006. When the honeymoon inevitably ends, Rudd will still be in a strong position if Labor support simply falls to 2006 levels.”

Many Labor supporters are still spooked by the experience of 2001 and 2004, where substantial early leads were turned around before polling day. But this Nielsen result is well ahead of anything that Labor recorded in 2004 (see the graphs at OzPolitics). And while it put Labor as high as 60% in April 2001, Rudd would have to be very unlucky for a second Tampa to appear over the horizon.