There will be no Labour government if it involves a coalition or a deal with SNP, Ed Miliband has said.
The Labour leader told BBC Question Time he "couldn't be clearer" there would be no deals between the parties.
SNP leader Nicola Sturgeon said Mr Miliband would never be forgiven if he let the Tories retain power rather than work with her party.
- Responsibility "triple lock": fully funded manifesto, cut the deficit every year, balance the books as soon as possible in next Parliament
- Extra £2.5bn for NHS, largely paid for by a mansion tax on properties valued at over £2m
- Raise minimum wage to more than £8ph by 2019
- No rise in VAT, NI or basic and higher rates of income tax
- Access to childcare from 8am-6pm for parents of primary school children
- Freeze energy bills until 2017 and give energy regulator new powers to cut bills this winter
With polls suggesting Labour could lose a number of its seats to the SNP on 7 May, Mr Miliband was repeatedly asked whether his party would work with Nicola Sturgeon's party.
"I am not going to have a Labour government if it means deals or coalitions with the Scottish National Party," he said, ruling out a so-called confidence and supply arrangement.
"It's not going to happen. I couldn't be clearer with you."
He added: "If the price of having a Labour government was coalition or a deal with the Scottish National Party, it's not going to happen."
Ms Sturgeon, UKIP leader Nigel Farage and Plaid Cymru's Leanne Wood were also being questioned in separate programmes.
Ms Sturgeon said people would be appalled by Mr Miliband's refusal to consider a deal with her party.
"He sounded as if he was saying that he would rather see David Cameron and the Conservatives back in government than actually work with the SNP," she said.
"Now, if he means that then I don't think people in Scotland will ever forgive Labour for allowing the Conservatives back into office.
With the first question of the special election edition of Question Time, Mr Miliband was challenged over the note left by former Labour chief secretary to the Treasury Liam Byrne for his successor, which said "there's no money".
He said the note was David Cameron's "regular prop" and that it was his party's "mission" to eliminate the deficit.
Citing comments by shadow chancellor Ed Balls that Mr Byrne's note had been a joke, an audience member said "running a business is anything but a joke", saying someone working in the private sector would be fired if they did the same.
Mr Miliband said his party was "deadly serious" about balancing the books.
He was also challenged by a man in the audience who said it was "ludicrous" he did not accept Labour had spent too much in government.
Labour had "got it wrong" on bank regulation, Mr Miliband said, adding that his party did not "do enough on apprenticeships" or on a "modern industrial strategy".
Speaking on Friday, Labour's general election co-ordinator Douglas Alexander accepted Mr Byrne's note had "not been wise" but said it was the "global financial crisis" which had caused the deficit to multiply, not the actions of the last government.
"Lehman Brothers did not collapse because Gordon Brown built too many schools and hospitals," he told BBC Radio 4's Today Programme.
Mr Alexander, who risks losing his own Paisley and Renfrewshire South seat to the SNP, said it would be a "disaster for Scotland" if the nationalists swept the board, suggesting it would let the Conservatives back into Downing Street.
"The SNP does not want to help the Labour Party, it wants to harm the Labour Party," he said, adding that his party would "not trade away the safety of the country" in any post-election discussions.
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