Labour leader Jeremy Corbyn has again failed to lay out the maths behind a huge spending splurge that will include a million new homes and £500bn in infrastructure investment.
However, he was unable to specify the growth levels that would be required in order to make the programme workable.
“We need a growth rate that would obviously continue to increase government income in order to pay for it,” Corbyn said.
“It's very hard to predict what the growth rate would be. At the moment it's very low, we're looking at one per cent or two per cent at the very most that we can achieve in the near future.”
Corbyn added that this economic growth, and boosted tax income would also help to pay down the UK's deficit, although he admitted that in order to do so would require a lot of improvement from current levels.
“It is low at the moment, it is one of the faster in the G7 but it could go a lot faster. We have the lowest level of investment of any G7 country and we're pretty low on the overall level,” he said.
Both Smith and Corbyn agreed on the need to invest in the economy, with the former admitting that in the short term that would see the deficit increase.
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However, Smith denied a suggestion that his promises “do not add up”, arguing that he had pledged to raise £13.5bn through taxes including a top level income tax of 50p, a one-off wealth tax, a 20 per cent corporation tax and reversals of planned reductions to inheritance tax and capital gains tax.
This money, Smith said, would go towards ending a public sector pay freeze and boosting NHS investment.
“All of the infrastructure spend I have talked about would be through raising an extra £200bn in borrowing,” he said. “It's crucial that we invest, we can't afford not to.”