Ed Balls was today accused of 'letting the cat out of the bag' on tax rises after leaving the door open to trapping more middle-class workers in the 40p tax rate. In an interview the shadow chancellor repeatedly refused to rule out trying to balance the books by lowering the amount workers have to earn before they pay the higher income tax rate. The number of people paying 40p tax has already risen from about 2million to 5million in two decades, but the Tories have promised to lift the threshold if they are returned to power. Scroll down for video . Shadow chancellor Ed Balls, pictured giving a speech in Glasgow today, has repeatedly refused to rule out using the point at which the higher income tax rate kicks in to raise money to balance the books . The Shadow Chancellor was joined by the Scottish Labour Leader Jim Murphy at the Royal Concert hall in Glasgow today . Labour has vowed not to increase VAT or National Insurance as part of measures to bring down the deficit if they win the election. But pressed on income tax, Mr Balls refused to rule out freezing or lowering the threshold to raise millions from people earning more than £41,865. In an interview on ITV Westcountry, Mr Balls was asked if was 'leaving the door open tonight to changing the tax thresholds that mean people in that 40 per cent bracket could be paying more tax under you'. The shadow chancellor refused to rule it out: 'What I would like to do is find ways in which I could have fewer people in the 40 per cent tax bracket. Of course I would. 'But I have to be honest with people. The deficit is going to be £90 billion. I have got to find a way to get the deficit down in a careful, and staged and balanced way.' He said he would not be 'raising the higher rate of income tax' but left open the possibility of holding or lowering the point at which it kicks in. 'What I cannot do is go through every detail of the tax system. It's really complicated. 'I am not going to make unfunded commitment to do so, because I fear in the end that will be a VAT rise from the Tories. You won't get that from me.' Pressed on whether he plans to change the income tax bands, Mr Balls said: 'I can't go through every detail.' He went on: 'I can make a promise not to increase the basic rate of income tax or the higher rate of income tax. The threshold is also an important detail and that's complex.' Chancellor George Osborne, visiting the Marston's Brewery in Wolverhampton with David Cameron today. claimed Mr Balls had 'let the cat out of the bag . The number of people paying 40p tax has already risen by about two million to five million in two decades . Chancellor George Osborne said: 'Ed Balls has let the cat out of the bag and confirmed a tax assault on middle earners. He has confirmed that he and Ed Miliband will put up taxes on middle Britain. It is part of Labour's £3,000 tax rise for working families. 'By contrast, the Conservative plan is to increase to £50,000 the threshold at which people pay the higher rate of tax. So there is a clear choice. 'Economic security and lower taxes with David Cameron and our long-term economic plan. Or economic chaos and higher taxes under Ed Miliband.' David Cameron has warned the 40p tax rate is hitting too many people on 'middle incomes'. The Prime Minister claims it is wrong that millions of people doing normal jobs like teaching are now paying a tax rate that was 'only ever meant for the better off'. The Conservatives go into the election pledging to raise the threshold for paying 40p tax from £41,865 to £50,000 by 2020. Workers would also pay no income tax on the first £12,500 they earn. But Labour says the policy is a £7billion unfunded tax cut at a time when billions are needed in spending cuts. A Labour spokesman said: 'Under the Tories around 2 million more people have been dragged into the 40p tax band, but Labour supported the increases in the 40p threshold in the recent Budget. 'Tory promises to raise the 40p threshold further are completely unfunded and will cost billions of pounds. Together with their extreme spending plans, these unfunded commitments will mean the Tories end up raising VAT again and cutting the NHS. 'When we make tax promises, such as introducing a lower 10p starting rate of tax to help millions on middle and low incomes, we have set out where the money is coming from. 'Working people are paying more under this government, which is why the only tax changes we are proposing are on the very richest in society like reversing the Tory tax cut for millionaires.'
Shadow chancellor refuses to rule out using threshold to raise money . Vows not to hike income tax rate but not trapping more people in 40p rate . Chancellor George Osborne says Balls has 'let the cat out of the bag . Tories promise to raise threshold from £41,865 to £50,000 by 2020 . Labour says the plan amounts to a £7billion unfunded commitment .