Tumim became chair of the NCVO in 1996 and left in 2001. In the role, she led the NCVO's campaign for reform of charity law, which she and others regarded as considerably out of date by four centuries. Tumim knew of a plethora of resistance to change in the charity and law worlds but concluded a revamp was needed. Her report was sent to the Blair ministry's strategy unit in 2002. which had considered change and agreed. Tumim's recommendations led to the passing of the Charities Act 2006, which introduced a definition of "public benefit" and revised public collection regulations. She was chair of the Forum on Children and Violence, which was formed after the 1993 Murder of James Bulger to campaign for investigations into what caused violence amongst children.