Finance Act 2003 introduced a 4 year time limit as regards claims for repayment of tax made on or after 1 January 2005. In addition, the right of the Revenue Commissioners to raise assessments was also reduced to a four-year period except where, for example, a taxable source of income was not declared. The scheme of 4 year time limits is designed to achieve the necessary balance between establishing a fair and uniform system for taxpayers, while at the same time, providing the necessary protection for the Exchequer from exposure to claims going back many years. As the 4 year time limit is set out in statute, the Revenue Commissioners have no discretion in the matter.