We now know that J Edgar Hoover, Head of the FBI, was politically regressive, deeply in the closet and vicious about it. He stood for everything Benjamin Britten opposed. Not a love match then. That Claggart business may have more meaning than we think.
Some years ago Donald Mitchell, the eminent Britten scholar, was doing some research under the Freedom of Information Act and came across a letter signed by Hoover himself in 1942 condemning Peter Pears, and another from 1967 condemning Britten. In both cases, the "evidence" is heavily blacked out. "A strange footnote", writes Mitchell, "a rare insight into a disreputable feature of 20th century politics in America and nearer home". It's cited in the Cambridge Companion to BB, ed Mervyn Cooke, where you can see photos of the original papers.