As Paymaster General, Primarolo was responsible for the administration of the Tax Credits system, which was a system that contributed to raising millions of children out of poverty. However, the administration of this system received some criticism, including allegations that some families were left less well off as a result. In 2003, a Treasury select committee member accused her of "losing control of department" after it became known that Inland Revenue buildings under Primarolo's purview had been sold to tax-haven companies. This came shortly after she had "insisted ... the Child tax credit scheme was a 'success'", despite Inland Revenue staff walking out in protest against the pressure under which they were placed. She was also responsible for introducing the controversial IR35 tax rules which were designed to tax "disguised employment" at a rate similar to employment. The measure was controversial as it was seen by some as unfair. Primarolo was also the longest serving Paymaster General in the office's 200-year history. Primarolo was named Chairman of the Code of Conduct Group upon its establishment by ECOFIN in March 1998.