The tide goes out slowly, but it does go out.

National and its dwindling supply of allies have almost exactly the same level of support as the left-leaning combination of Labour and the Greens, our latest poll of polls shows. This result mirrors the individual results of two TV polls, both published yesterday, showing a very close result.

We estimate that the Maori Party would hold the balance of power if an election were held today, with both the left and right blocks picking up 58 seats. With New Zealand First holding over 4% at this point in the cycle, however, only a great fool would say it will definitely, of even probably, miss out on seats at the next election. Should New Zealand First ease up to 5-6% then it would hold the balance of power instead of the Maori Party. (New Zealand First would need 5% rather than 4% because the Electoral Commission’s proposed reforms to the electoral system, even if enacted quickly, will almost certainly not take force until the 2017 election.)

If that happens, then any government would require at least three parties to at least not oppose it in confidence votes, and a National-led administration would likely require five parties (National, ACT, United Future, the Maori Party, and New Zealand First). Given what John Key has said previously about the dangers in “multi-headed monster” governments, that situation would not make him at all comfortable.

Our “now-cast” – the fancy word people use now when they want to say “poll-based seat calculation” – also gives seats to the three small party leaders currently holding electorates. In at least one case (ACT), and possibly more, this is probably an overly generous assumption. More realistic assumptions in this area would probably hurt National’s cause more than the left’s.

Just as important as the two-years-before-the-election snapshot is the trend line in support, which has clearly favoured the left through 2012. At the last election, the left-right polling gap was around 11%. At the start of 2012 it had dropped to around 5-6%. Now it is zero. These linear trends will not, of course, extend all through the next two years. But the substantial right-to-left movement over the past twelve years clearly shows increasing dissatisfaction with National’s performance in government, and increasing support for a centre-left alternative coalition based around Labour and the Greens.

Even more than the individual results over the weekend, that trend is David Shearer’s friend, and John Key’s enemy.