- Since the referendum vote, the SNP has been riding a wave of unprecedented popularity
- One opinion poll sees the party taking all 59 parliamentary seats in Scotland
- If either of the main UK parties fails to secure overall majority, this would put SNP into strong position
(CNN)Six months ago, it was a political party that had lost.
The Scottish people had decisively rejected independence from the United Kingdom in a referendum that the Scottish National Party demanded.
SNP leader and Scotland's first minister Alex Salmond -- who for more than 20 years led the Scottish nationalists from a fringe interest to the country's government -- resigned. His party's dreams of a sovereign Scotland looked in tatters.
At the time, the leaders of the UK's main political parties -- Labour and the Conservatives -- must have thought their worries about Scotland were over for a while.
But what has emerged, as the UK prepares to vote in a general election on May 7, is quite the opposite.
Since the referendum vote, the SNP has been riding a wave of unprecedented popularity.
In March, membership of the SNP officially passed 100,000, in a country with an estimated population of 5.3 million.
If the polls are right, the Scottish National Party could take the bulk of the seats in Scotland at voting time.
Nick Anstead, a specialist in political communication and elections at London School of Economics, says the SNP has been tactically clever. "They've managed to appear to be both an insider and an outsider party," he says.
"They run a government in Scotland and they get to act like outsiders in the context of Westminster politics."
The Scottish National Party, currently the ruling party in Scotland, was formed in 1934, with Scottish Independence as its central principle. In 1998, following a vote in favor of devolution by the Scottish people, a Scottish parliament was created with powers to make laws on a range of issues.
The national government in Westminster retains control of issues like foreign policy, defense and immigration, but Hollyrood has authority over issues like health and tourism for Scotland.
The Scottish National Party's soaring popularity is also a legacy of the 2014 independence referendum campaign.
"Scotland went into the referendum with an independence party but came out with a movement," says Iain Macwhirter, a political commentator and author of "Disunited Kingdom: How Westminster Won a Referendum but Lost Scotland."
"That's led to a genuine sea change in political attitudes in Scotland -- and a determination by the 45% (of Scots) who voted (for independence) to translate that into votes for Westminster," he adds.
If they do, it could be a game-changer in British politics.
At the time of writing, Scottish Television projects the party could win all 59 parliamentary seats in Scotland. A win of those proportions would be earth-shattering -- in the 2010 election they took six seats and their previous all-time high was 11 in 1974.
The knock-on effect in Westminster of the SNP's new-found power could be substantial. It would take most of the vote in Scotland from the left-of-center Labour Party, currently the party of opposition in the UK, possibly wiping out Labour's presence in a former heartland.
A SNP landslide would also fragment Labour's vote, meaning that even if it won enough votes across the rest of the country to win the election, it would still need another party to form a government.
"At the moment, it looks like it's very hard to construct a majority (in government) without them," says Anstead.
There are 650 seats in the UK Parliament, and the party that controls more than half forms a government. Notably, in the last election in 2010, neither Labour nor the Conservatives won enough votes to go it alone, so a coalition government was formed by the Conservatives with the Liberal Democrats.
This time around, there has been a surge in support for parties like the UK Independence Party and the Green Party -- although it remains to be seen how this translates into seats.
These parties have traditionally had little representation in Parliament, and any support they win nibbles away at votes that would traditionally have gone to either the Conservatives or Labour.
And skyrocketing support for the SNP in particular means it would be the likely kingmaker of a coalition government.
That is particularly troublesome for the Conservatives, since Nicola Sturgeon, leader of the SNP, has said her party will "never, ever" go into a coalition with them.
She has gone as far as to say that she wants an "anti-Tory" majority in Westminster with the Labour Party that can work towards a politics that is "something better, bolder and more progressive."
In response, Britain's right-of-center parties have gone on the offensive with rhetoric about the risks of a deal between Labour and the SNP, saying that a party that wants to break up the UK would effectively be put into a position of dominance.
Boris Johnson, the Conservative Mayor of London said it would be a recipe for disaster and called Sturgeon a "scorpion," compared her to King Herod the baby killer and one tabloid called her "the most dangerous woman in Britain."
But the SNP is not making life easy for the Labour party either. Crucially, it says it won't go into a coalition with Labour -- but has not ruled out a looser agreement.
One way it could do it is with confidence and supply government that would allow the SNP to maintain a Labour government in power in a less formal way.
"It (would give) them power to extract concessions on a vote by vote basis," says Anstead.
Sturgeon has accused Labour of being Tory-lite and has said she will "embolden" the party if the SNP finally gains real power in Westminster.
Labour leader Ed Miliband has been quite clear that there is no possibility of a deal. "I want to be clear about this. No coalitions, no tie-ins ... I disagree with them on independence," he told the BBC.
All this just adds to the multiplicity of possible outcomes in what is proving to be the most unpredictable election the UK has seen for many years.
Back in Scotland, people aren't worried about any of this. In offices and pubs and on the street, the Scots have a renewed sense of confidence.
"The independence vote woke everybody up," says Jonathan Kane, 40, a restaurant/bar owner who lives in Edinburgh. He voted for independence in the 2014 referendum.
"I realized that nobody really knew that much about politics until the independence debate -- and that's across the whole spectrum of the people I meet in the pub," he says.
But over the past two years, he adds, people have gotten a lot more switched on to economic and political issues.
Kane adds: "That's why I think a massive drive is happening now: Because people who maybe weren't pro-independence are now (thinking) let's just vote SNP because we'll have more say.
"No one would have predicted: 'Let's all vote No and shake up Westminster.'"