Ed Balls has attempted to bolster Labour's economic credibility by ruling out higher borrowing to pay for its programme if it wins power.
In his keynote speech to the party's final conference before the general election, the shadow chancellor warned that with the deficit still running at £75 billion he would have to make "unpopular" decision, in a sobering reminder that austerity would still continue.
Balls' decision to extend his pledge not to raise borrowing to capital spending suggests further cuts will be needed to pay for his infrastructure and housing promises.
Previously Labour had said it would hold current spending down, but left open the possibility of borrowing more to fund infrastructure and housing projects. Concern has been expressed by shadow cabinet members that Labour's reluctance to talk about cuts resulted in voters thinking the party was not serious enough about keeping the public finances under control.
Ed Balls has moved to make this pledge in a bid to help his party persuade voters for next year's general election that it can be trusted with the economy. Balls and Labour leader Ed Miliband have regularly trailed George Osborne and David Cameron in polls over who is most trusted to run the UK economy, with a recent poll putting the lead enjoyed by the Tories on this at 25%.
Speaking to activists in Manchester, Balls said he would stick to "fiscal responsibility in the national interest".
Speaking on the BBC's Daily Politics, shadow chief secretary to the Treasury Rachel Reeves said: "We are planning to get the national debt down, which means you have to be running a surplus to be able to do that.
She added: "If you are going to have national debt falling you have to have a surplus overall ... To get debt falling you have to have a surplus on overall spending."
The Tories seized on Reeves' comments to attack Balls' pledge as Labour would only run a surplus on current spending.
Business minister Matthew Hancock said: "Rachel Reeves has let the cat out of the bag. She has backed the Conservatives’ plan to deal with our debts, not Labour’s. She admits that the only way to get ‘debt falling’ is to ‘have a surplus on overall spending.
‘As the Institute for Fiscal Studies say, Ed Balls’ policy means £28.3 billion more borrowing per year in the next parliament.
"Labour haven’t learned their lesson. They would burden our children with more debt than our children could ever hope to repay."
This comes after shadow business secretary Chuka Umunna told activists that the party needed to build a "big tent" to win the forthcoming election campaign, which will be fought in a "bloodsport style".
He denied Labour was focused on a "35% strategy" aimed at getting the party just over the line in next year's poll.
"It is very important we don't draw the lesson (from the referendum) that we just focus on one part of our support," he said. "We have got to build a coalition and it's really important in the wake of that result."