Image copyright Reuters Image caption Sir John said he had an "absolutely duty" to warn about dangers to the union

Ex-PM Sir John Major has claimed that a Labour government supported by the SNP would be a "recipe for mayhem".

Sir John used a speech in the Midlands to say a Labour-SNP government would mean families paying with "higher taxes, more debts and fewer jobs".

He said a future Labour government would be subjected to a "daily dose of blackmail" from the nationalists.

But Ed Miliband said the Conservatives were putting the future of the UK under threat by talking up the SNP.

The Labour leader told BBC Breakfast Mr Cameron was "playing fast and loose with the union" and risked "setting England against Scotland". He should be "taking on, not talking up" the SNP, he said.

SNP leader Nicola Sturgeon described Sir John's comments as an "affront to democracy".

And there has been unease among former Cabinet ministers who served alongside Sir John in the 1980s and 1990s, Lord Tebbit suggesting the party's strategy was "puzzling" while Lord Forsyth said the attacks could backfire and threaten the "integrity" of the union.

'In hock'

In a speech in Solihull, Sir John said he had been warning of the risks posed to the union for 20 years and, as a unionist, he had an "absolute duty" to make sure voters understood the risk the SNP's influence would pose.

Media playback is unsupported on your device Media caption David Cameron: SNP intends to 'break up the country' if in power

"If Labour were to accept an offer of support from the SNP, it could put the country on course to a government held to ransom on a vote-by-vote basis," he said.

"Labour would be in hock to a party that - slowly but surely - will push them ever further to the left. And who would pay the price for this? We all would. We would all pay for the SNP's ransom in our daily lives - through higher taxes, fewer jobs, and more and more debt.

"This is a recipe for mayhem. At the very moment our country needs a strong and stable government, we risk a weak and unstable one - pushed to the left by its allies, and open to a daily dose of political blackmail."

Sir John denied his remarks "de-legitimised" any possible Labour-SNP government.

'Silly'

Referring to Ms Sturgeon, who is not standing for a Westminster seat, he insisted: "If you want to talk about de-legitimising, I would like to know what someone who isn't even a candidate for the House of Commons is doing talking about her party changing the policy and politics of the government of the whole of the United Kingdom," he said.

"That's what's de-legitimising."

Mr Miliband - who has rejected a Labour-SNP coalition - dismissed claims that the SNP would "call the shots" in the event of a hung parliament.

"It ain't going to happen," he said.

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Ms Sturgeon said: "John Major's comments are silly, over the top and, frankly, they don't show him in a particularly good light.

"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."

Media playback is unsupported on your device Media caption Ed Miliband: David Cameron "threatening the integrity" of UK by "talking up" SNP

Recent polls all point towards there being a hung parliament after 7 May, and suggest the SNP could be the third largest party and crucially hold the balance of power.

As a consequence of this, the "threat" of an SNP link-up with Labour has emerged as a major Conservative line of attack in the election campaign.

Image copyright AP Image caption Ed Miliband has ruled out a coalition deal with the SNP

Sir John said the SNP's "driving ambition" was an independent Scotland, and it would use its position to demand policies that favour Scotland at the expense of the rest of the UK.

"That is no way to run a country. And nor is it remotely fair to England, Wales and Northern Ireland," he said.

'Scare tactic'

But former Conservative chairman Lord Tebbit said his party's tactics were a distraction from their "primary task which is to elect Conservative members of Parliament".

Media playback is unsupported on your device Media caption The Scottish Liberal Democrat leader Willie Rennie launches his party's election manifesto saying it is a "choice between the Lib Dems and the SNP"

He suggested the logical conclusion of the Conservatives' arguments was that people should vote Labour to keep the SNP out as "the lesser of two evils" in the majority of Scottish seats where the Conservatives are unlikely to win.

"I think it's a huge scare tactic against Labour," he told BBC's Newsnight.

"Having bungled the Scottish referendum it seems pointless to just irritate Scots by shouting at them from Westminster. The English are irritated into voting for UKIP by being shouting at from Westminster - and the Scots are irritated similarly."

He added: "I just cannot read Mr Cameron's mind. It's a foreign country to me."

And former Liberal Democrat leader Lord Paddy Ashdown accused Sir John of having a "fit of amnesia" about the troubles he experienced as prime minister between 1990 and 1997.

"If there's any prime minister of Britain who will know what it's like to be held to account and indeed be run on the basis of bribes given every day by the extremists, it's Mr Major, who had 16 bastards - he called them bastards, that's his word not mine - in his party," he told the BBC.

He claimed the Conservatives now had 60 "extreme right-wingers" in the party "who will make Mr Cameron weak, just as they made Mr Major weak", and who were in "an unholy alliance with UKIP and the Ulster Unionists".