FIVE months out from the last Holyrood election, a poll put Labour 16 points ahead of the SNP. Iain Gray's party had enjoyed other double digit leads over Alex Salmond's nationalists, who had formed a minority administration after gaining just one seat more than their rivals in 2007, over previous months.

That convincing lead, it transpired, would be wiped out. The SNP won an unprecedented majority in 2011, delivered on its pledge of holding a referendum on independence which, despite losing, contributed to an electoral tsunami last May that saw the party win all but three of Scotland's Westminster seats.

With just a few months to go until the 2016 election, and pollsters predicting that the SNP is on course to better even its remarkable success of 2011, could a similar reversal be on the cards that would propel Kezia Dugdale into Bute House? It is hugely unlikely, if the experts are to be believed.

Monthly polls for TNS has put the SNP at no lower than 56 per cent in the constituency ballot since last May, with a high, in July, of 62 per cent. The most recent suggested that the nationalists would take 78 of Holyrood's 129 seats.

John Curtice, a professor of politics at Strathclyde University and the UK's most respected pollster, said that while their remained some scope for opposition parties to make inroads, the SNP's challengers faced an uphill struggle in the light of a new "dividing line" in Scottish politics.

He said: "There will be no shift in the polls unless Labour, or perhaps the Tories, can persuade people who voted for independence to no longer support it or that if they are in favour of independence, that they don't have to vote for the SNP. The challenge is to break that link.

"There is material there - Scotland's fiscal position now would not be as rosy as it would have been 12 months ago. There is also the question of the SNP's record in Government. However, Labour will have to come up with a platform that begins to excite people. They can say the council tax freeze benefits the rich more than the poor, but unless they propose an alternative it falls flat."

It has been suggested the real battle will be for second place. With Labour on course to lose all of the 15 constituencies it won in 2011 and rely solely on list MSPs, some polls have put Ruth Davidson's Conservatives within reach.

There are few signs of a LibDem revival, despite leading scrutiny of Police Scotland at Holyrood, with one of the stories of the election potentially a rise of the Scottish Greens. The party has benefitted from the referendum with membership surging from 1,500 to about 9,000 bringing with it new talent, cash and activists.

The issues on the table will also, for the first time, include significant powers over tax and spending with Holyrood set to gain control of income tax rates and bands, along with some welfare powers.

Tom Costley, the head of TNS Scotland, said his organisation's research had indicated a "very stable and significant" lead for the SNP, which it had maintained despite scrutiny over domestic issues.

He added: "Unless the other parties in Scotland can succeed in convincing the public that the performance of the SNP Government has been poor in those important devolved areas such as the health service and education, the only issue to be determined will be the size of the SNP majority in the parliament after May 2016."