Labour would expose 'sweetheart deals' by forcing firms to publish tax returns
Large firms would be forced to publish full tax returns under Labour plans to expose "sweetheart deals" and tackle avoidance.
The proposal would apply to firms with more than 250 employees and follows criticism of the tax affairs of giant companies.
Shadow Chancellor John McDonnell said the measure would help close down "loopholes and scams".
HM Revenue and Customs estimates the tax gap - the shortfall between tax collected and what might be expected - at £36 billion, with £9.5 billion attributed to large companies.
Labour also highlighted the estimated £13 trillion worldwide hidden in tax havens and claimed that if the Exchequer could receive a fraction of this amount it would end austerity.
Mr McDonnell said: "Tax avoidance is a scourge on society that company secrecy laws help facilitate, and the Tories have done nothing to tackle.
"Labour will pour the disinfectant of sunlight on large company accounts, helping close down the loopholes and the scams that the tax dodgers rely on.
"The Tories are running a rigged economy for the super-rich and giant corporate tax dodgers. Only Labour will stand up for workers and small businesses to make our tax system fair and our public services like education and the NHS protected."
Under Labour's plans the requirement to file tax returns at Companies House along with annual accounts would apply to firms with a turnover over £36 million, a balance sheet over £18 million or more than 250 employees.
Labour argued that w hilst large companies may be able to hire accountants and lawyers, "wine-and-dine senior civil servants and other policymakers", many comparatively small companies are not in a position to secure any "sweetheart deals".
The publication of large company tax returns and related correspondence would expose any such deals, the Opposition said.
When Parliament returns after the Easter recess on Tuesday, Labour will also push to strengthen measures to tackle tax avoidance in the Finance Bill.
Shadow chief secretary Peter Dowd said: "The measures in the Finance Bill claiming to close tax loopholes do not go far enough and have gaping omissions, another Tory conjuring trick to hide their inaction in making sure that everyone, including the rich, pays their fair share of society's upkeep.
"There is nothing in the Government's proposals to address the chronic lack of enforcement in the context of the wider regulatory problems. As usual, the Tories are playing rhetorically to the gallery."
Conservative Party vice-chairman Stuart Andrew said: "This Government has a simple message for those who avoid tax: You must pay what you owe and we will make sure you do.
"After 13 years of Labour doing nothing we have led the way on tackling tax evasion, avoidance and non-compliance, securing an additional £140 billion in additional tax revenues since 2010.
"All Labour would do now is wreck the economy with higher taxes, half a trillion in additional borrowing and a leader who says we should not be afraid of debt."