The Scottish Labour leader Jim Murphy has criticised David Cameron and Sir John Major over their attacks on the SNP.
Campaigning in Glasgow today, he said:
John Major and David Cameron have given up on the Scottish Conservative Party and are giving their all to the SNP. The Tory Party no longer has its own independent campaign in Scotland but has become an active campaigner for the SNP.
The Tories are making it clear by their words and their deeds today that David Cameron can only be saved by Scotland voting SNP
Sir John Major's warning about the threat the SNP could pose to the UK is an "affront to democracy", Scotland's First Minister said.
Nicola Sturgeon hit out at the former Conservative prime minister's remarks, after he intervened in the midst of a General Election campaign which has put the SNP in the political spotlight.
Ms Sturgeon hit back, insisting: "Some of the comments we're hearing in the media this morning from Tory politicians like John Major are actually an affront to democracy."
John Major's comments are silly, over the top and frankly they don't show him in a particularly good light.
My message to John Major is Scotland's voice deserves to be heard in whatever way the Scottish people choose, and voting SNP means Scotland's voice will be heard more loudly and strongly at Westminster than it has ever been heard before.
But it will also be a voice for better and more progressive politics at Westminster, so perhaps it's not surprising that John Major doesn't like that. But what he is saying disrespects democracy, it's up to people in Scotland to vote how they choose to vote and make their voice heard.
David Cameron has dismissed criticism about his tactics in relation to the SNP.
Speaking at a PM Direct event in Leeds he said: "All I am doing is pointing out what is as plain as the nose on your face - which is, right now, Labour is facing a wipe-out in Scotland."
Sir John Major said that Nicola Sturgeon talking about the SNP changing the policy of the government delegitimises a Labour coalition - as she is not a candidate for the House of Commons.
The former Prime Minister was answering a question from ITV News Correspondent James Mates:
The Tory party has a heart former Prime Minister John Major has said.
Throwing his support behind David Cameron's campaign Sir John said: "I gave my lifetimes work to the Conservative party because I know them from the inside and they do care and they do help. They may not wear their heart on their sleeve, but it beats just as strongly to help people as the heart of any other political party in this country."
We will never all be born equal. Life isn’t like that. But it is the Conservative mission to make opportunities in life as equal as we can make them.
That is what first drew me to the Party nearly six decades ago. While Labour was, generously and big-heartedly, offering me a hand “out”, the Conservatives offered me a hand “up”.
Today there are many young people now who are people who are in just the sought of circumstances that I was then. They need a hand up as well.
Former prime Minister John Major said the Labour party have a history of ruining the economy.
Sir John, speaking in West Warwickshire said:
They blame the financial crash – but all one needs to do is pick up a history book. Every single Labour government we have ever had – from Ramsay MacDonald to Gordon Brown – has ruined the economy. Every single time.
There’s a pattern. Labour wrecks the economy. The Tories repair it but become unpopular in doing so. Labour are re?elected and wreck it again. It’s time to break that pattern.
Ed Miliband accused David Cameron of "threatening the integrity of the United Kingdom" by talking up the prospects of Scottish nationalists in the General Election.
The Conservatives are stepping up their campaign on the dangers of nationalist influence by deploying former Prime Minister Sir John Major to deliver a stark warning that a minority Labour government propped up by SNP votes would be a "recipe for mayhem".
But Mr Miliband insisted there would be no coalition with the SNP and denied Nicola Sturgeon's party would hold the whip hand on policy, telling BBC1's Breakfast:
A Labour government led by me, what happens in that Labour government will be decided by me, not by the SNP.
I think David Cameron is playing fast and loose with the United Kingdom.
This is somebody who has given up hope of winning a majority. He is trying to boost the SNP. I think David Cameron is now threatening the integrity of the UK with the games he is playing. And I think Conservatives are now ashamed of what he is doing.
Former Liberal leader Lord Steel says Sir John Major does not understand Scotland.
He told the BBC Radio 4 Today programme:
The Tories are really doing the SNP a favour by bringing them to the centre stage of the campaign.
I think the consequence is we will end up with a minority government. Ed Miliband has made it clear he does not want any deal with the SNP.
With 16 days to polling on May 7, Sir John will say in a speech in the Midlands that a Labour-SNP administration would lead to "weak and unstable" government and wreck Britain's economic recovery.
Nicola Sturgeon says it would be her - rather than her predecessor, Alex Salmond, or the SNP's leader in Westminster, Angus Robertson - who would lead any coalition negotiations after an inconclusive election result, despite not standing for a seat in the House of Commons.
She told the Daily Mail: "I'll be there. I'm the leader of the SNP, I'll be in charge of any decisions and negotiations and anything that happens after 7th May."
Ms Sturgeon also indicated that a second independence referendum for Scotland could be triggered if the UK votes to leave the EU in 2017.
She said a "substantive change in circumstances" would be needed to re-run the poll, adding: "If there was a vote that ended up taking Scotland out (of the EU) against our will - that's the only concrete example."