Jeremy Hunt has pledged to cut national insurance again in the autumn “if we can afford” it.
The chancellor has lowered the tax twice since he entered Number 11, which the government says has saved people an average of £900 a year.
But speaking at an event in London on Friday, he said “we’re not stopping there”, adding: “If we can afford to go further to responsibly reduce the double tax on work this autumn, that is what I will do.
“We make no apology for wanting to keep cutting the double tax on work until it’s gone, but only when we could do so without increasing borrowing and without cutting funding for public services or pensions.”
Politics live: Hunt attacks Labour in tax speech
Mr Hunt has said he plans to abolish NI entirely at some point in the future, claiming it is “unfair that we tax work twice” when other forms of income are only subject to one levy.
But Labour has attacked the Conservatives for failing to explain how they would pay for the move – which it estimates will cost £46bn – saying it could “lead to higher borrowing, higher taxes on pensioners or the end of the state pension as we know it”.
Answering questions from reporters after the speech, Mr Hunt condemned Labour’s remarks as “nonsense” and “fake news”, adding: “Our ambition has no time commitment because we’ve been explicit that we will only deliver it when it can be afforded. It will come through growth in the economy and not by increasing borrowing or cutting spending.
“It is frankly disgusting to try to scare pensioners by misrepresenting that policy.”
He instead claimed Labour had £38bn of unfunded spending pledges for the next parliament that could only be covered by raising taxes.
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“Taxes will go up under any future labour government, as sure as night follows day,” the chancellor said.
“But taxes will go down under a Conservative government because we will do the hard work necessary to keep our economy competitive.”
However, he would not guarantee a timescale for such reductions.
Mr Hunt told Sky News: “If you’re saying can I look into a crystal ball and predict what is going to happen in the world in the next five or 10 years, and therefore give you a cast-iron guarantee of when we will be able to reduce the tax burden and to what level? The answer is, of course I can’t. And it would be irresponsible to do so.
“That is why, by the way, our commitments to abolish the double tax on work – employees’ national insurance – we haven’t put a time limit on it because it will depend on factors that are beyond our control, such as the overall growth in the economy as to when we can afford it.
“But my commitment is that the tax burden will go down under a future Conservative government.”
Mr Hunt also refused to commit to lowering tax thresholds if the Tories stayed in power – something dubbed a “stealth tax” by government critics, as more people move into paying tax as wages increase, but thresholds stay the same.