British Prime Minister David Cameron's Conservative Party is one point ahead of the opposition Labour Party before Thursday's election, according to a poll carried out by research firm Opinium and published on Wednesday.

The poll put Cameron's party on 35 per cent, unchanged from a previous Opinium poll, and Labour also unchanged at 34 per cent.

Support for anti-European Union UKIP fell one point to 12 per cent, the Liberal Democrats were unchanged at eight per cent and the Greens rose one point to six per cent, Opinium said.

Meanwhile, opinion polls suggest that the Scottish nationalists are set to crush their opponents north of the border and the supporters are now fiercely argueing the party's role in Britain's future political landscape on the eve of the United Kingdom's parliamentary election.

The pro-independence Scottish National Party (SNP) leader Nicola Sturgeon, riding a tide of popularity, pledged that her party would work for the good of all Britons, not just Scots.

Speaking to a crowd in Edinburgh, Sturgeon said that Scots and English voters who favoured progressive politics and an end to austerity should unite against the Conservative Party.

"If we work together we can lock out the Tories. We will work with others across the United Kingdom, that is my pledge," she said.

Cameron made a rare visit to Scotland to warn of what he saw as the dangers posed by the SNP, while his partner in the ruling coalition, Liberal Democrat leader Nick Clegg, also travelled north in what appeared to be a forlorn hope of propping up support for his party.

The SNP is set to take all but a handful of the 59 Scottish seats in the 650-member British parliament, a scenario that has caused panic in the two main parties.

With the Conservatives and Labour running neck-and-neck in polls, the SNP could be the king-maker in a hung parliament.

However, Labour leader Ed Miliband has ruled out a coalition with the SNP while Cameron has said the SNP having a powerful position in Westminster would be a nightmare which could lead to the break up of the United Kingdom.-Reuters