The government has been forced to admit an error in the calculation of tax and national insurance relief paid on pensions contributions.
It has emerged that the inaccurate estimates could amount to £20 billion.
The Office of National Statistics revealed recently that its estimates for pension contributions qualifying for tax relief would be revised down from £58 billion to £46 billion
The Conservatives have rounded the government, claiming that the error highlighted the government's "complacency".
"Tax relief on pension contributions has been worth less because pension contributions have been smaller than the government thought," Tory pensions spokesman David Willetts told the Telegraph newspaper.
The pensions crisis is one of the government's biggest challenges.
At the Labour Party conference last week, pensions secretary Alan Johnson told delegates that he would be taking personal responsibility for resolving the issue.
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