One of the few constant features in Britain's modern political landscape has been the high level of support for the Scottish National Party (SNP).

Opinion polls indicate it will, once again, scoop the biggest number of Scotland's 59 parliamentary seats at Westminster in the General Election on Dec. 12.

In the 2007 Scottish Parliament elections, it narrowly overtook the Labor Party to form a minority government in Edinburgh. This was turned into a majority four years later. Then, the SNP eclipsed Labor in the U.K. General Election of 2015, more than doubling its share of the popular vote to 50% while increasing its tally of MPs at Westminster from six to 56.

In the most recent U.K. General Election two years ago, the other major parties – particularly the Conservatives – did recover a little in Scotland, although the SNP still retained 35 seats and more than one-third of the votes.

Since then, the Scottish Nationalists have been skillfully exploiting the fact that the majority of Scottish voters in the 2016 referendum on leaving the European Union opted to "remain." The ardently pro-EU SNP loudly complains that its nation – as part of the U.K. – now risks being taken out of Europe by the pro-Brexit majorities in England and Wales.

This grievance glosses over an inconvenient fact: In 2014, the people of Scotland voted by 55% to 45% in an independence referendum to remain in the U.K. rather than to separate from it. This means, among other things, they have chosen to participate in and be bound by the decisions of all national elections and referendums. Instead, the SNP has done everything possible in the courts and parliaments to prevent Brexit implementation.

Its campaign to portray Scotland's future outside the EU as an unqualified catastrophe has been echoed by much of the Scottish media and most political parties except the Conservatives.

Labor's support then collapsed in Scotland following the 2010 election of a Conservative-led regime in London whose austerity and privatization policies have been overwhelmingly rejected by the Scottish electorate. Scottish Labor's failure to offer a clear left-wing alternative allowed the SNP to pose as the real champions of the people, offering a vision of an independent Scotland in which the Conservatives could never win office.

In the 2015 General Election, Labor held on to only one of its Scottish seats, while the Liberal Democrats were punished for their part in the Conservative-run coalition and lost ten of their eleven MPs in Scotland.

Thus, the SNP has come to dominate the political struggle in Scotland.

How very different things were for much of the 20th Century. After the end of the First World War in 1918, Labor and the Conservatives fought a long battle for Scottish electoral supremacy. The latter enjoyed a strong base among Scotland's own capitalist, landowning and professional classes.

However, between 1964 until 2010, Labor commanded by far the biggest share of parliamentary and local council seats and votes. This reflected the party's strength in the central industrial belt stretching from the Ayrshire coalfields and shipyards and engineering works of "Red Clydeside" in the west to the Fife and Lothian coalfields in the east.

Apart from one short-lived seat in the House of Commons, the SNP had little impact on parliamentary politics for the first 33 years of its existence. Created by the merger of two smaller nationalist parties in 1934, its leadership was drawn from Scotland's own establishment of lawyers, academics and minor aristocrats. In a period of sharp class conflict, the party's campaign to repeal the 1707 Act of Union with England struck most industrial workers as irrelevant, even if emotionally appealing.

Then, Winnie Ewing won the Hamilton parliamentary by-election in 1967. Support for Labor was on the slide, as Scots reacted against industrial decline, central government neglect and Labor complacency. The Labor Party's response was to establish a Royal Commission on the Constitution and promise to set up a Scottish assembly or parliament.

A surge in support gave the SNP 11 MPs in 1974, as it turned a little to the left politically. However, when the Labor government's devolution plans failed to win a big enough majority in a rigged referendum, the Scottish Nationalist MPs helped bring it down and thereby opened the door to the conservative government of Margaret Thatcher in 1979.

Consequently, the SNP lost two-thirds of its votes and all but two of its seats in the House of Commons. More recently, the party has climbed back up to the top of the electoral tree, from where it claims to espy the promised land of an "independent" Scotland inside the EU.

The party's policy is to demand a second referendum on independence as soon as possible. However, this would need the consent of the government at Westminster.

A Labor government would probably agree to hold such a poll should the demand persist, but not until 2021 at the earliest, when Labor would campaign against the break-up of Britain. The Conservatives oppose holding a second referendum at any time in the foreseeable future.

Opinion polls indicate that the people of Scotland are almost evenly divided on the question of separation from the U.K., with a slight majority against. The Labor, Liberal Democrat and Communist parties favor federalism as a solution to the national question in Britain.

Moreover, the SNP has yet to answer some difficult questions, primarily: how genuinely "independent" would Scotland be as a small member state on the fringe of the EU? How would an SNP government pursue its anti-nuclear weapons and non-militarist defense policies now that the party has abandoned its opposition to NATO membership?

How could Scotland exercise fiscal and monetary self-government while retaining the pound – controlled by the English Treasury – as its national currency? What kind of "withdrawal agreement" would be reached with London, allocating more than 300 years of shared assets and liabilities between them? What cross-border commercial and trading arrangements – and at what cost – would be negotiated with Scotland's biggest economic partner by far, England, with one country inside the EU and the other outside?

The SNP may believe that British withdrawal from the EU is too costly, damaging and complex to be allowed to proceed, but Brexit could be a leisurely walk in the park compared with a Scottish exit from the U.K.