Ed Miliband said he could be "a prime minister who unites the whole of our country" as he hit back at "desperate" Tory claims a Labour government would be forced to rely on Scottish nationalist votes.

The Opposition leader repeated his insistence that he was "not interested in deals" with the SNP in the event of a hung parliament after the General Election - and insisted his party could defy the polls to win in Scotland.

He insisted voters were more interested in issues such as the economy, the NHS and immigration, accusing the Tories of having "given up" campaigning on those in favour of a negative campaign.

He hit back after David Cameron warned voters that they had "11 days to save Britain", as he claimed Scottish nationalists "don't want the country to succeed".

In an escalation of his rhetoric about the dangers of the May 7 General Election producing a minority Labour government propped up by the Scottish National Party, the Prime Minister told the Sunday Express that nationalist MPs would be hoping for a "disaster" which would bring forward their dream of independence.

Conservative Home Secretary Theresa May told the Mail on Sunday that a Labour/SNP government could be "the biggest constitutional crisis since the abdication", when King Edward VIII gave up the throne in 1936.

And London mayor Boris Johnson said the prospect was "very deeply alarming" - suggesting Mr Miliband would have the SNP "crouching on his back like a monkey" if he made it to Number 10.

The latest opinion poll in Scotland showed Labour remained on course for heavy losses to the Scottish nationalists in its heartlands north of the border - keeping hold of as few as five of the 41 seats won in 2010.

Just over a quarter (27%) of Scots say they will be voting for Labour in the election, according to the Panelbase poll for The Sunday Times, down two on earlier in the month, with the SNP up three points to stand at 48%, the research found.

Mr Miliband insisted his party could still turn that around and win in Scotland, telling the BBC1 Andrew Marr Show: "I think we can."

"We've got challenges in Scotland but I have an old fashioned view which is 12 days before an election you allow people to vote and then we'll see what the outcome is," he said.

He denied that ordinary voters were concerned about a Labour/SNP deal, telling the programme: "That's not what I'm picking up."

He said: "The Tories and the SNP now have something in common: they want to set one part of the country against another. The Tories say it's England versus Scotland; the SNP say it's Scotland versus England.

"We need a prime minister who can unite the whole of our country, who can stand up for working people in every part of the United Kingdom and that's the prime minister I believe I can be.

"The challenges that we have in common across our country are bigger than what divides us.

"The Conservative and Unionist Party used to believe that but they are so desperate they are reduced to trying to set one part of the country across another."

The latest set of national polls indicated that the General Election race was still neck and neck, with the UK heading for a probable hung parliament and coalition negotiations after May 7.

Pressed on whether he would consider a confidence-and-supply deal with the SNP to ensure backing for a Queen's Speech and Budget if he failed to secure an overall majority, Mr Miliband said: "I am not interested in deals, no."

"If it is a Labour government it will be a Labour Queen's Speech, it will be a Labour Budget. It will not be written by the SNP."

Mr Miliband defended his party's proposal to prevent private landlords raising rents by more than inflation over the course of a three-year tenancy deal.

The policy - part of a package of measures designed to help the growing numbers unable to afford to buy and stuck in rented accommodation - was dismissed as "drivel" by Mr Johnson who said it would cut housebuilding and result in significant hikes at the end of each three years.

The Labour leader said the proposals were not the same as discredited Labour "rent control" policies of the 1970s and had been proved to work over recent years in Ireland, where rents had not been inflated to allow for it.

"We've got families who don't know from one day to the next whether they are gong to be kicked out of their home or if their rents are going to be jacked up by 10%.

"That is not good enough for the Britain that I plan to lead," he said.

"There are always people - special interests, Boris Johnson - who say we can't have that change because they want to defend the status quo. But this country needs to change so it works for working people again."

Defence Secretary Michael Fallon said: "Ed Miliband can duck, dive and refuse to answer the question as many times as he likes.

"But the simple fact is that he can only be Prime Minister with the support of SNP votes in the House of Commons - a new poll only today shows that it's impossible otherwise.

"It's the British people who will pay for a Miliband-SNP deal with higher taxes, higher spending, higher welfare payments and weaker defences. It would wreck our economy and take our recovery back to square one."