"This prime minister would wreck the recovery by putting a tax on every job, on everyone earning over £20,000, a tax on aspiration, a tax on every business in the country," he said.
Earlier Mr Brown said business leaders who backed the Tory plans had been "deceived" and Mr Cameron used prime minister's questions to quote others who criticised government policy on pension funds and the armed forces - and ask if they had been "deceived" as well.
Ocado founder Tim Steiner, Asos chief executive Nick Robertson, Monsoon's Peter Simon and Yell chairman Bob Wigley are the latest to publicly back the Tories' pledge to scrap the bulk of the NI rise.
The Tory leader said the final Commons clash ahead of the general election was the "last chance for this prime minister to show that he is accountable for the decisions he has made".
On issues such as military equipment and pension funds, he said Mr Brown "takes no responsibility and blames someone else".
Mr Brown said the NI rise would protect investment in schools, police and NHS guarantees, while the Conservatives would "put hospitals, police and our health service at risk" - claiming they would take £6bn out of the economy.
ANALYSIS OF COMMONS CLASH
Colette McBeth, BBC political correspondent
So what did we learn? Well, David Cameron thinks Gordon Brown is a master of deception, who's hoodwinked the public on funding for helicopters in Helmand and robbed pension funds.
Then he pulled out his joker - announcing another 30 business leaders were supporting Conservative plans to block National Insurance rises. The Conservatives know Labour don't want to pick a fight with business, which is why they are keen to stoke one.
But Gordon Brown said it was all about a choice. You could raise NI contributions and protect public services or you could cut them and schools, policing and hospitals would suffer. You couldn't have it both ways. To much merriment, he threw David Cameron's famous line to Tony Blair back at him: "You were the future once."
Nick Clegg was angry. He told them they'd both failed, colluding in blocking reform to our political system. "It's time to go" he said.
This is what we will hear over and over again in the next few weeks. It's all about a choice. Who do you trust with political reform, public services and the money in your pocket?
"We can't cut our way to recovery," Mr Brown said.
BBC business editor Robert Peston said the row over NI represented "an ideological difference" between the two main parties.
He said Labour wished to raise NI to pay for public services, while the Conservatives want to reduce the size of the state.
Mr Brown also pledged on Wednesday not to raise the basic rate of tax - currently 20 pence - if re-elected.
The disagreement over NI came as the parties each highlighted their plans for political reform - including changes to the voting system - a subject which has been increasingly discussed in the wake of the MPs' expenses scandal.
Lib Dem leader Nick Clegg accused both parties of "trying to fool people they are serious about political reform" - when they had failed to agree reform of party funding.
And he criticised the government for failing to deliver on 1997 promises for a "new politics": "Look at them now: You failed, it's over, it's time to go," the Lib Dem leader said.
Mr Brown later outlined new plans to hold two referendums - one on changing the voting system and one on reforming the House of Lords - if Labour wins the election.
He also pledged to introduce fixed-term parliaments and give people the right to "recall" MPs guilty of "gross financial misconduct" before a general election, to ban MPs from lobbying and force them to get outside jobs approved by an independent body.
David Cameron taking questions from bakery workers in Bolton
The proposed changes, which Mr Brown said would be the most "comprehensive" for 100 years, have been interpreted by some as an attempt to appeal to Lib Dems should he need their support in the event of a hung Parliament.
Mr Brown told the BBC's Nick Robinson it was "up to the people" whether he would share power with another party after the election while insisting he was "fighting for a victory".
The Conservatives accused Labour of "tinkering" with the electoral system to their own advantage and say what people really want is fewer MPs and ministers and the right to get rid of corrupt MPs.
Throughout the day parties have stepped up campaigning across the country.
Answering questions from bakery workers in Bolton, Mr Cameron said the decline of manufacturing under Labour had been a "tragedy" and he pledged to expand apprenticeships and technical schools.
On a later visit to Cardiff, Mr Cameron said he hoped the Conservatives would become a "much, much larger" party in Wales after the election, building on its success in last year's European elections when it beat Labour into second place in the overall vote.
Visiting Liverpool, Mr Clegg said the Conservatives' pledge to protect low and middle earners from tax rises was a "bit of a con" and that only millionaires would get tax breaks under the Tories.
Meanwhile, Mr Brown answered questions at an internet forum in London and later canvassed voters by phone.
The prime minister was heckled by a member of the public as he was climbing into a car. The man demanded to know why he could not get his son into the school of his choice.
Asked why he had not spoken to the man, Mr Brown said he was "happy" to answer questions at public meetings but was on his way from one engagement to another at the time.
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