FOUR senior Tories made a dramatic intervention in the General Election campaign yesterday, provoking a furious response. Former Prime Minister Sir John Major stepped up warnings about the outcome of the election, which opinion polls have suggested could see the SNP win as many as 50 seats and hold the balance of power in the Commons.

Major predicted “mayhem” if the poll results in a Labour government propped up by the SNP.

However, Nicola Sturgeon branded his comments “an affront to democracy”.

Former Scottish Secretary Lord (Michael) Forsyth and Lord (Norman) Tebbit, a former party chairman and minister in Margaret Thatcher’s Cabinet, also entered the fray, turning on their own leadership’s tactics. Later, Sir Malcolm Rifkind, the former Secretary of State for Scotland, urged Scots Tory supporters to vote

Labour in order to keep out the SNP.

Major said Ed Miliband’s only route to 10 Downing Street involved a pact – whether in coalition or an informal and unacknowledged partnership – with the SNP, who he warned would subject the Labour leader to “a daily dose of political blackmail” pushing him “slowly but surely ... further to the left”.

He said the SNP would use the position to demand policies favouring Scotland at the expense of the rest of Britain, driving a wedge between the nations of the UK, hoping to win the 2016 Scottish Parliament election and paving the way for a second independence referendum.

“They will ask for the impossible and create merry hell if it is denied,” he warned. “The nightmare of a broken United Kingdom has not gone away. The separation debate is not over. The SNP is determined to prise apart the United Kingdom.”

Arguing it would be “perverse” for the electorate to remove Conservatives from office as recovery was taking hold and the country needed stable government, Major urged even the “disaffected, disengaged [and] downright fed-up” voters in the key Tory target seat of Solihull to give David Cameron another term.

Sturgeon said the comments were “an affront to democracy”.

“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,” said the SNP leader.

Labour’s Alistair Darling, who led the No campaign against independence, said the Tories were “flirting with English nationalism” in a “desperate” way that could lead to another period of divisive wrangling over Scotland’s position.

However, Major dismissed suggestions that he was stoking up division by demonising the SNP as “classic Labour spin”.

Forsyth said in a newspaper interview that his party’s tactic of targeting a Labour-SNP link-up was a “short-term and dangerous game” and could ultimately damage the Union.

“We’ve had the dilemma for Conservatives, which is, they want to be the largest party at Westminster and therefore some see the fact that the Nationalists are going to take seats in Scotland will be helpful,” he said.

“But that is a short-term and dangerous view which threatens the integrity of our country.”

Scottish Tory leader Ruth Davidson told the BBC: “I think Lord Forsyth has fallen into a bit of a Nationalist trap here by framing this as a Scotland versus England thing, and it is not. Unionists across the whole of the UK are concerned and frightened about the sort of concessions that the SNP being in charge of a weak Labour government could bring and whether those concessions would put the UK – that I fought for, that many people fought for, that we won a referendum on – at risk.”

Tebbit – a long-time critic of Cameron – described the Prime Minister’s repeated warnings about the SNP as “puzzling” and “pointless”, and said they may push Scots Conservatives “to vote tactically for Labour”.

The focus on the SNP was “not helping Mr Cameron’s prime task, which is to elect Conservative members of Parliament”.

He said the Prime Minister did not have a “hinterland” of experience, unlike previous generations of politicians who were “real men”, such as ex-premiers Winston Churchill or Clement Attlee.

“I think it’s a huge scare tactic against Labour and whether the particular seat in the House of Commons is occupied by a Labour member or an SNP member perhaps it’s not a great difference,” he said. “Having bungled the Scottish referendum, it seems pointless to just irritate Scots by shouting at them from Westminster.” He added that “the risk to the Union comes from the SNP, not from anyone else”.

Cameron brushed off criticisms of his approach, telling an event in Leeds: “All I am doing is pointing out what is as plain as the nose on your face – right now, Labour is facing a wipe-out in Scotland.”