Protecting the economic recovery "matters more than anything", David Cameron declared as he hit back at critics of his General Election campaign in a passionate rallying cry to Tory activists.

In a punchy speech, he defended the decision to focus on risks posed to the economy by Labour and the SNP, insisting there was no "lack of drive" and saying claims he favoured the wealthy should be stuck "where the sun don't shine".

With no sign of either main party ending the deadlock in opinion polls, Mr Cameron has faced internal sniping over what has been perceived by critics to be a lacklustre campaign.

Ed Miliband accused him of having "given up" on key issues such as the NHS and immigration in favour of a "desperate" focus on the potential for Labour relying on Scottish nationalists to govern in the event of another hung parliament.

The Opposition leader was promoting Labour plans to help private tenants by curbing real-terms rent increases and renewed his insistence that he was "not interested in deals" with the SNP despite falling further behind in polls north of the border.

But Mr Cameron said those who accused him of "playing it a bit safe" ignored the central issue facing the electorate.

"I have been Prime Minister these last five years. If people are saying to me we are putting too much emphasis on a strong and stable economy and in securing our future, I plead guilty," he told activists in Somerset.

"If you think economic security and stability don't matter, if you want to take a risk, go with the other guy, vote with the other man. By God he's got plenty of risks," he said.

"He has found ideas that haven't worked anywhere in the world and he has put them in a book. It's called the Labour manifesto.

"I'm not going to put the British economy at risk, I'm not going to put the stability of Britain's families at risk, that is what is at stake in these last 11 days."

He said Conservatives "don't always shout with the passion that some people would like.

"But don't mistake that for any lack of drive in changing this great country of ours and making it greater still.

"We are the only people that can stop the prospect of Ed Miliband and the SNP teaming up and wrecking our economy and taking us right back to square one."

"If you want political theatre - go to Hollywood," he told critics.

"If you want political excitement maybe you could go to Greece, that's a very exciting country I'm told, every day government having to take money out of one part of government to pay people in another."

In contrast, he said, people getting jobs, coming off benefits, getting the keys to their first home, starting a new business, graduating and starting an apprenticeship were "the things that make my heart beat a little faster".

"In this election you are going to hear all sorts of grand schemes and ideas and ideologies. It doesn't amount to a hill of beans if you can't provide jobs, livelihoods, growth and the things that deliver for people."

The PM - who has already expressed his anger at Labour claims that his Government has benefited the rich at the expense of ordinary voters - did not mince his words over his feelings on that score.

"I want you to think about the three million low-paid people we have taken out of income tax, I want you to think about the two million jobs that we have created, I want you to think of the cuts in youth unemployment that we've achieved," he said.

"I want you to think of that and I want you to take that argument that Labour make and stick it where the sun don't shine.

"It wasn't the rich and the bankers that suffered under Labour - they kept their knighthood, they kept their bonuses, they were fine.

"It was the poorest in our country who suffered from Labour. It was them who lost their jobs, their livelihoods. They didn't help the few, they hurt the many and we will never let them forget it."

Mr Cameron - who was campaigning in the seat being defended by Liberal Democrat minister David Laws - hit out at his coalition government partners for saying they were "equally" likely to form a deal with Labour next time.

He told them: "You cannot give these people a second chance with the British economy and the safety and security of people's lives".

And, repeating warnings that a Labour government supported by the SNP would divert funding from English regions, he took a swipe at its former leader Alex Salmond, who hopes to make a return to the Commons next month.

"How much time do you think Alex Salmond thinks about Somerset? I don't think he could probably find it even with a compass and a map," he said.

Mr Miliband said he could be "a prime minister who unites the whole of our country" after Mr Cameron warned voters they had "11 days to save Britain" because Scottish nationalists "don't want the country to succeed".

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.

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."

But SNP leader Nicola Sturgeon told Sky News: "I suspect Ed Miliband will change his tune once the votes are cast."

Mrs May had made herself look "completely and utterly stupid", she said.

Chancellor George Osborne said the rent-cap proposals were a "totally economically-illiterate statement that yes, grabs headlines, but is dismissed by every expert who looks at it".