McCormick's reliance on an informal network of oral informants, and his eye for a good story, means that it is often difficult to judge the reliability of his more controversial claims. In 1979 he claimed that Rudolf Peierls had been under investigation as a Soviet agent, and was forced to make an out-of-court settlement when Peierls sued him. (The equally controversial Rupert Allason, who once worked for McCormick, has continued to press this particular claim after Peierls's death.) McCormick also claimed that the early-twentieth-century economist Arthur Pigou had been a Russian agent, and to be in possession of Pigou's journal: no such journal has surfaced since McCormick's death.