The big news in the Sunday papers, and what may well prove to be the game-changing moment of the campaign, is that the SNP has moved ahead of Labour in both the constituency and regional section of the polls.

The figures are:

SNP – 40%/35%
Labour – 37%/33%
Conservatives – 11%/12%
Lib Dems – 8%/7%
Greens – -/6%

In terms of seats (and using the same methodology from my half of #SP11 Regionwatch) I make that to be (constituency/regional):

SNP – 33/21 = 54
Labour – 37/12 = 49
Conservatives – 1/13 = 14 (only FPTP seat being Ettrick, Roxburgh & Berwickshire, a 1,334 majority over SNP)
Lib Dems – 2/4 = 6 (majorities of only 711 and 1,164 in Orkney and Shetland respectively, both from the SNP)
Greens – 0/5 = 5 (2 in Lothians, 1 in Glasgow, 1 in H&I and 1 in MS&F)
Margo – 0/1 (my base assumption is that Margo will be comfortably re-elected)

Key FPTP wins for the SNP would include: Aberdeen Central (maj of 829 over Labour), Almond Valley (maj of 664 over Labour), Ayr (maj of 129 over Labour), Cunninghame North (maj of 572 over Labour), Edinburgh Pentlands (maj of 340 over Labour), Glasgow Southside (maj of 453 over Labour), Linlithgow (maj of 413 over Labour) and Stirling (maj of 150 over Labour)

That’s not to mention Airdrie & Shotts (SNP 165 votes short), Clydesdale (SNP 657 votes short), Edinburgh Eastern (SNP 16 votes short of Labour), Glasgow Kelvin (SNP 759 votes short of Labour)

A 5 seat winning margin may seem strong but there are more tight victories in my model for the SNP than there is for Labour so if Labour close the gap over the next few weeks and if a few of the above FPTP wins for the Nats are reversed then where does that leave us?

Well, keeping only Glasgow Southside as SNP gains or holds in the first list there and moving Aberdeen Central, Almond Valley, Ayr etc back to current incumbents, while keeping everything else in the model from this poll fixed, then the result becomes:

SNP – 52 (26/26)
Labour – 52 (42/10)
Conservatives – 13 (3/10)
Lib Dems – 7 (2/5)
Greens – 4 (0/4)
Margo – 1

So, neck and neck between Labour and the SNP with the Conservatives intriguingly holding the balance of power. The above also highlights the advantages for Greens in voting tactically for the SNP in many regions, finishing now with 4 seats rather than 5 (losing the 2nd Lothians MSP) whereas the Lib Dems conversely move up to 7 from 6 (picking up a second list MSP in North East).

However, this is not to take away from a remarkable achievement from the SNP, borne out of two main strategies

(1) – pitch the second vote as a vote for who should be First Minister (which it isn’t, this is a parliamentary election, not a Presidential one)
(2) – sell Salmond (and this poll only include 30%-50% of the impact of the SNP manifesto launch and Salmond’s impressive BBC Question Time performance as the fieldwork was Wednesday to Friday)

So, it’s a stellar result for the Nats at just the right time and that momentum is growing. The SNP were 8/1 to win most seats at the start of the year when Labour were streets ahead in the polls, the SNP were 3/1 to win most seats on the evening of the STV debates and today those odds are only 5/4. Being the official odds on favourites for Holyrood 2011 surely beckons and what then for Iain Gray?

SNP voters can now effectively be split into two, there is the ~25%-30% baseload SNP voter that has stuck with the party for at least the majority of the past four years, willing to back the party if asked by a pollster. Then there are the recent converts, the Scots who intend to vote SNP today but would have voted for another party months or even weeks ago.

The key question for me now is not so much what has changed but what would have to change over the next few weeks for those voters to go back from whence they came, and let’s assume that that is back to Labour.

Wheeling out Gordon Brown, as will be the case this month, will not make much of a difference, the election isn’t about independence so attacking the SNP on that score isn’t an option and on policies such as apprenticeships, free education, renewable energy and council tax freezes, Labour policies are more to do with damage limitation than outdoing the SNP in any way. So I really do think Scottish Labour’s options for victory are closing to a point that inevitability around a May 5th defeat isn’t far off.

The only potential fix that a clearly panicked Labour group may go with is to push even harder the clearly flawed message of ‘Tories at Westminster means you need Labour to protect you’. The fear-mongering, the negativity that has cost them before, most notably in 2007, might be enough to scare a few former loyal supporters back into line but it would be desperate stuff. Furthermore, if we really are past the tipping point, then such a negative message could only serve to increase the SNP majority as individual voter behavious becomes a group phenomenon. This ‘now that the Tories are in power’ mantra is a message that Labour has chosen to put at the front of its manifesto and it is linked to many of the key quotes in the press recently. It may come to symbolise the next stage of this campaign but I personally can’t see it working as the mesage is getting mixed.

At the end of the day, voters want to know what they’re getting from who they vote for and the SNP message is clear – five year Council Tax freeze, no nuclear power and a drive towards 100% renewable electrical power by 2020. Easy to understand and easy to digest. The same is largely true of the Greens (public transport a higher priority, raise revenue to offset cuts, no Forth Road bridge) and Lib Dems and Tories.

Labour’s key themes seem to be a focus on cancer waiting times, facing up to David Cameron and a two year freeze on Council Tax. It just doesn’t gel right somehow and, crucially, it doesn’t seem enough to get those lost votes back.

Alex Salmond and his team may well be joyously sliding down the electoral mountain over the next few weeks and, for once, the most important poll may not be the next one, or the one after that or even the one on May 5th. To all intents and purposes, it may prove to be this one if it turns out that the next time Labour lead in a Holyrood poll on either the constituency or regional vote is some way far off in the distance.

And finally, tactical voting considerations – this poll predicts a clean sweep of 10 FPTP constituencies for the SNP in the North East, a region where my model predicts 4 Labour lists MSPs and 0 Green MSPs. Even with 9 FPTP constituencies for the SNP there seems little chance of the party winning a list MSP. Is it worth SNP voters considering voting tactically for a fellow anti-nuclear party? Have the Nats finally found what Glasgow is to Labour and will it have the savvy to use that local opportunity to full advantage?