Labor promises to return the budget to ''modest'' surplus in 2016-17. In the interview, the Opposition Leader acknowledged that tax revenues in the next term of government could fall short of Treasury forecasts, as they have done six times since the 2010 election.

Tony Abbott would accept Labor's mandate to implement its planned emissions trading scheme if it won the election. Credit:AP

''We've said that Labor will never deliver a surplus and if the projections turn out to be accurate, we'll deliver a surplus at least by the relevant date of 2016-17, but that's if these projections turn out to be correct,'' Mr Abbott said. ''Let's hope they do but given the record you wouldn't be surprised if they don't.''

Mr Abbott said: ''[Treasury] think there are enormous downside risks to the projections and we just don't know where it's all going to end up.''

Putting priority on the Coalition's spending promises over its intention to return to surplus, he said: ''While I accept that things can come up, there's nothing that an incoming government should or would do that violates our mandate because the thing that has most alienated people over the last six years and particularly over the last three years is a government which appears to have no respect for the commitments that it has solemnly entered into the day before. We've just got to keep our commitments.''