U.K. election 2015: Polls show campaign going down to the wire

Britons cast their ballots Thursday and all signs point to the result being a minority government or "hung parliament," as they say across the pond.

After governing in a coalition with the centrist Liberal Democrats since 2010, British Prime Minister David Cameron's Conservative Party is at risk of losing its hold on power.

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The Conservatives have averaged about 33.5 per cent support in the last week of polling in the United Kingdom, a drop from the 36 per cent the party captured in 2010. The centre-left Labour Party, led by Ed Miliband, is just behind with an average of 33 per cent support. That represents a gain of four points since the party lost power under Gordon Brown five years ago.

Nick Clegg's Liberal Democrats were the surprise of the 2010 campaign, when they surged in the polls to challenge Labour for second place. In the end, support slumped to 23 per cent on election day. But after forming a coalition with the Conservatives, support for the Lib Dems plummeted dramatically. It hasn't rebounded since, and current polls award the party just 9 per cent support. That would be its worst performance in 45 years.

The polls have been remarkably steady throughout the election campaign, with neither Cameron nor Miliband able to break the deadlock.

Complicating things for those two leaders is the rise of the Scottish National Party and the United Kingdom Independence Party.

The SNP, after narrowly losing its bid for independence last year, is soaring in the polls. Four recent surveys awarded the party an average of 48 per cent support in Scotland, against just 25 per cent for Labour. That is a significant shift since 2010, when Labour took 42 per cent of the vote to the SNP's 20 per cent.

The 50 seats the SNP is expected to win blows a large hole in the electoral map Miliband would need to form a majority government without a coalition partner.

The Greens, jumping from 1 per cent in 2010 to 5 per cent in the polls, also limit Miliband's growth potential.

But if Labour is being squeezed out in the north, the Conservatives are suffering elsewhere on the right.

UKIP, a Eurosceptic party that is also suspicious of immigration, has risen to 13 per cent in the polls after taking just 3 per cent of the vote five years ago. Though their vote has softened of late (the party was flirting with 20 per cent late last year), UKIP eats into the Conservatives' potential vote considerably.

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Coalition or minority?

Much talk during the campaign has been about whether Cameron or Miliband will be able to cobble together a majority coalition after the vote is held. Seat projectors in the U.K. give the Conservatives about 280 seats and Labour about 270. Both fall well short of the magic number of 326 needed for a majority.

The Liberal Democrats are expected to win some 25 seats, less than half the 57 they won in 2010. That means the Conservative-Lib Dem coalition will not have the numbers to form a majority government again. They have a few dance partners in the parties running in Northern Ireland and maybe even UKIP, but still, the incumbents are likely to fall short.

Miliband could potentially form a coalition with the Lib Dems and Greens, but that would still not be enough. Instead, the partner most talked about is the SNP.

The pro-Scottish independence party has ruled out any coalition or support for the hated Conservatives, but is willing to prop up Labour. While workable within the House of Commons, it might not pass muster with voters. Relying on the SNP for power would be little different for Miliband than it was for Stéphane Dion and Jack Layton to rely on Gilles Duceppe's Bloc Québécois when the Liberal and NDP tried to form a coalition government in 2008. Canadians know how that turned out.

The real outcome of the election, then, may be only known long after the votes are counted. If the seat totals make for no easy majority for either Cameron or Miliband, negotiations with the other parties will be fraught. One or the other may even try to govern with a minority. It is a situation that may become very familiar to Canadian voters this fall.

This article reviews trends in public opinion surveys. Methodology, sample size and margin of error if one can be stated vary from survey to survey and have not been individually verified by the CBC.