Mistakes which have left more than a million people facing extra tax payments are linked to massive job cuts in the Inland Revenue, a union leader has claimed.
Mark Serwotka, general secretary of the Public and Commercial Services union, said there is a link between the current crisis and the loss of around 30,000 jobs since the Inland Revenue merged with Customs and Excise in 2005.
"There are not enough workers in the department, checks are not taking place, people cannot get through to contact centres because of the sheer volume of calls.
"There are a million pieces of paper yet to be dealt with which is building up problems. The department brings in money and should be stuffed with staff."
Mr Serwotka, speaking in Manchester ahead of this week's TUC gathering, said £27 billion of taxes was uncollected because of a lack of resources.
"This is a good example of how the Government's spending cuts are economically stupid," he added.