In a 2010 publication Jurrie Reiding asserts that Debye may have been an MI6 spy. Reiding discovered that Debye was befriended by the well-documented spy Paul Rosbaud. They first met around 1930 when they were both working as editors for two scientific journals. They collaborated in the escape of Lise Meitner in 1938. According to Reiding, Debye was well connected in German scientific and industrial circles and could have provided MI6 with valuable information. For example, as board member of the German Academy for Aviation Research he was acquainted with Hermann Göring. Reiding also offers an explanation for Debye's hasty departure on 16 January 1940 for the United States: the date coincided with the planned (but later delayed) German invasion of the Netherlands a day later, information possibly provided to him by Rosbaud.
This hypothesis is contested by Philip Ball, as he notes that friendship with Rosbaud is no gauge of Debyes political stance. Rosbaud was well-connected with many people and Debye, while he was a friend of Rosbauds, seems to have also felt regard for geologist Friedrich Drescher-Kaden, an ardent Nazi.