ALL non-SNP seats in Scotland, 53 out of 59, are now marginals with the outcome on May 7 uncertain, according to analysis by the Electoral Reform Society.

Although the General Election is four weeks away, the ERS says its new analysis shows that the winners in more than half of all the seats across the UK can be safely called; of a population of 60m, some 26m people live in safe seats.

But while the campaign group says it can confidently predict the winners in 364 of the 650 seats, 56 per cent of the total, based on how "safe" they were in 2010 and in line with current national and local opinion polls, it notes that this is not the case in Scotland.

Of the 303 Conservative seats, the ERS concludes 186 are safe, of the 257 Labour seats, 150 are safe, of the 56 Liberal Democrat seats, just seven are safe and of the SNP's six seats, five are safe.

The ERS, which campaigns to replace the traditional First-Past-the-Post system at Westminster with Proportional Representation, says: "In the case of Scotland, due to the unpredictability created by the large poll swing towards SNP since 2010, all non-SNP seats have been classified as marginal."

It adds: "We can predict that 42 per cent of the seats in Scotland will be won by men - 25 of the 59, whereas only three will definitely be won by a woman. Indeed, 13 seats only have men standing; across all the parties."

Willie Sullivan, the Director of ERS Scotland, said: "The 2015 election may be exciting and unpredictable in Scotland but it remains the case that the First-Past-The-Post voting system will result in a disproportionate result and that most voters only have two choices; SNP or Labour.

"Voters across Scotland are grappling with a choice between tactical voting and voting for what they believe in. Every vote could count if we had a fairer voting system," he added.