THE question of whether Scotland will follow the road to independence with Nicola Sturgeon's SNP remained the defining – and for now at least unanswered – question in Scottish politics in 2016.

For the SNP, the year ended as it began with the party remaining the dominant force in Scottish politics, albeit with a slight chink in its armour due to the largely unexpected loss of its overall majority at Holyrood.

But despite this small erosion in the SNP's position, pro-independence parties continue to hold sway, with a majority in the Scottish Parliament that could yet see a bill voted through for a second independence referendum and make 2017 the year that such a vote is triggered.

Despite the lack of an explicit manifesto commitment to "indyref2", the SNP's third Holyrood election win left the prospect open, since the party's pre-election manifesto had stated that a change in “material circumstances” could lead to a fresh independence referendum.

Such a change in circumstances took place less than two months after the Holyrood vote, when Scotland voted 62-48 to Remain in the EU, but was narrowly outvoted by the UK as a whole and left facing the prospect of being dragged out of the EU against the nation's will.

There was also the oft-stated argument made by SNP big-hitters in the first half of the year that each constituent part of the UK ought to have its own particular vote in the EU referendum respected, something the Tory Government categorically and uncompromisingly ruled out.

The day after the Brexit vote, Nicola Sturgeon said that a second independence referendum was now "highly likely", setting the mood music for the second half of 2016.

The First Minister's promise that her government would now begin preparing legislation for a second referendum meant the prospect of another vote on leaving the UK remained a potent possibility throughout the remainder of the year and into Christmas, when Sturgeon revealed some of the detail of her plan to keep Scotland in the single market.

However, 2016 also saw a hardening of the battle lines over the issue of independence, with the make-up of the Edinburgh parliament being determined to a large extent on the basis of the national question.

The fifth Scottish Parliament election delivered ample evidence of just how split down the middle Scotland now is on the constitutional question.

Although the SNP victory came as no surprise, the elevation of the Scottish Tories to official opposition status represented one of the most significant election results of the devolution era, perhaps the second most important after the 2011 SNP landslide that paved the way for the first independence referendum.

For Scottish Labour to be replaced by the party of austerity at Westminster as the supposed alternative government to the SNP was a devastating blow to a once pre-eminent political force north of the Border, from which it may never recover in Scotland.

Despite the humiliating drubbings handed out to Labour by the SNP in 2011 when Alex Salmond won his overall majority and in 2015 when the SNP took 40 Westminster seats from Labour, finishing behind the Tories is arguably a more cataclysmic and disastrous result.

Slumping into third place is also immeasurably worse than the initial loss of power to the SNP in 2007, as at least then Labour was still seen as the only viable alternative government to the SNP, and just three years later was still able to go on to win 41 seats in the Westminster election.

Yet May's election delivered a blow that even a few years ago would have seemed unthinkable for the party of John Smith, Robin Cook and Gordon Brown – to finish in third place behind a party that was led at Westminster by David Cameron and the self-styled "austerity Chancellor", George Osborne.

Scottish Labour leader Kezia Dugdale said she was "heartbroken" as her party was decisively pushed into third place in Scotland by the Tories for the first time in modern history – finishing behind a party that had, during New Labour's high watermark at the 1997 UK general election, been wiped out in Scotland.

In contrast, and to the horror of Scotland's progressives, Ruth Davidson led the Scottish Tories to their best parliamentary election result in well over half a century by making an unapologetic pitch to Unionist voters, stating that hers was the only party prepared to defend the Union with a "no to a second independence referendum" theme.

The strategy paid off in May's election, as the Tories outflanked Labour as defenders of the Union, with suggestions from the Tories that Labour could no longer be trusted to make the case against Scottish independence and that a "strong" Unionist voice was needed.

The result leaves us with a potential five-year fight being played out at Holyrood between the pro-independence SNP and the Unionist Tories, while Labour, whose raison d'etre is social justice, is squeezed in a parliament where the constitution is the battleground and where class-based and leftist politics is becoming marginalised.

This is unchartered territory for Scotland – where the conventional model is to have social democratic or left-of-centre parties vying with a centre-right party for power. Now, we are in a straight fight between a Unionist and a Nationalist party, albeit one that promotes a civic and progressive model of nationalism.

While such a model escalates the decline of Scottish Labour and marks another chapter in the party's ongoing misery, it's also a development that suits the SNP leadership, which can now confront a widely-hated Unionist opposition in the shape of the Tories – tied to Theresa May's government at Westminster – head-on.

The First Minister has not been slow to step up her attacks on Davidson, accusing the Scottish Tory leader in early December of being a "sell-out" over the Single Market and of being a born-again Brexit supporter.

Sturgeon said Davidson had abandoned the pro-EU stance she championed during the EU referendum and had instead adopted the hardline rhetoric of Westminster Tories such as Theresa May, Chancellor Philip Hammond and Foreign Secretary Boris Johnson.

It was perhaps the start of a narrative that will form a key part of the SNP's attack on the Tory opposition and may end up being similarly effective to the Labour-Tory alliance jibes Alex Salmond was able to direct at the Better Together campaign ahead of the 2014 independence referendum. Few words hurt as hard as "sell-out".

Trying to take on the SNP from the left may give Scottish Labour a flicker of hope of a revival. Although their chances look slim to non-existent, the party has made a relatively good fist of challenging the SNP to use its powers to renationalise rail services.

New powers promised to Scotland in the run-up to the 2014 independence referendum have now started to be devolved and the Scottish Government will soon be in a position to take decisions about welfare, giving ministers at Holyrood the chance to alleviate cuts made by Westminster.

Calling out SNP ministers on whether they will take such action could work for Labour – and for all Dugdale's difficulties there were signs late in the year that she was taking such an approach.

As always, though, with modern Scotland, it is the constitution that beats everything – and the First Minister's speech to the SNP conference in October, in which she vowed to call "indyref2" if the Tory Government delivers a "hard Brexit", proved to be the most significant announcement of 2016.

On the face of it, 2016 saw all the necessary ingredients fall into place for a second referendum, with a Tory Government with just one Scottish MP still ruling over Scots, and led by a Prime Minister who is distinctively of the southeast of England and was not even placed before the electorate in 2015.

Meanwhile, the ongoing likelihood of Scotland being made to live with the consequences of a Brexit it did not vote for has confirmed that, as the 2015 general election result made clear, Scotland and England are on radically divergent paths politically.

The winding down of the Yes Scotland campaign after the 2014 referendum has meant that there has been no consistent promotion of the case for independence, whereas conversely opponents of independence have had a field day, with most sections of the media vigorously promoting the UK.

The fact that support for independence remains at much the same level as on September 18, 2014 is remarkable in such circumstances and we would do well to remember that when Alex Salmond and David Cameron signed the Edinburgh Agreement in 2012, support for independence stood at less than a third.

This continuing support, and the ongoing threat of a "hard Brexit" imposed by a Tory government Scotland did not vote for, means that 2017 could well be seen as a pivotal year on the road to independence.