The Scottish National Party (SNP) could win 57 of Scotland's 59 seats in the British parliament in a May 7 election, according to a projection based on an opinion poll published on Monday.

The TNS poll, conducted in Scotland between April 1 and 19, found support for the SNP at 54 percent, while Britain's opposition Labour Party was on 22 percent, the ruling Conservatives on 13 and their Liberal Democrat coalition colleagues on 6 percent.

Due to the way Britain's first-past-the-post electoral system works, those percentages could result in the SNP winning 57 seats in the House of Commons in London, while Labour and the Liberal Democrats would win just one each, according to a projection by the website ScotlandVotes.

In the past, Scotland was a Labour stronghold. Labour won 41 seats there in the 2010 election, while the Liberal Democrats won 11, the SNP won six and the Conservatives one.

Labour and the Conservatives are level in most national polls, with neither on course to win an overall majority on May 7. That means that the SNP may hold the balance of power.

Labour has ruled out a post-election deal with the SNP, whose long-term goal is independence for Scotland.

TNS said support for the SNP had increased by two points since its previous poll, while Labour's support had decreased by two points.